Sleep is a physiologically induced, active state of unconsciousness characterized by decreased muscular tone, decreased sensory activity, and decreased engagement with the environment. Nowadays, people are unable to get enough sleep due to a number of life style factors leading to chronic sleep deprivation that can significantly impact mood, increasing irritability, anxiety, and depression. Conversely, good sleep promotes emotional well-being and resilience. In addition, adequate sleep is needed to perform best. Individual satisfaction, precise sleep timing, adequate length, high efficiency and constant alertness during waking hours are characteristics of a healthy sleep pattern (1). This leads to fatigue, slowed reflexes, and impaired decision-making, increasing the risk of accidents and injuries (2). On the other hand, side having a consistent sleep schedule, going to bed and waking up around the same times each day, helps regulate our sleep-wake cycle and promotes better sleep quality (3).

Human sleep displays a pattern that reflects their culture, society, physical health, emotions, mood, stress, geographical conditions, etc. (3). For instance, those who reside in higher latitudes sleep for longer periods than those who do not (4). Effects of sleep pattern disruptions might be either short-term or long-term. Short-term consequences include headaches, decreased immunity, mood fluctuations, difficulty concentrating, and impaired reflexes. Whereas long-term effects include a higher chance of developing chronic conditions like diabetes, obesity, and heart disease (5) increased chance of mental health issues such as anxiety and sadness. 

Human sleep patterns and schedules

Each person has different sleeping hours and ideal sleeping pattern. The choice of sleep pattern is based on a person's needs, genetics, and other variables including demographics. Certain patterns stated below are defined by research on sleep-wake cycles.

Monophasic sleep: The most typical sleep pattern worldwide is monophasic sleep, which consists of just one phase of sleep. Individuals who work 9 to 5 typically follow this type of sleep schedule.  For monophasic sleepers to get the necessary amount of sleep before beginning their day, they need seven to nine hours at night (6). Since the majority of individuals don't get the recommended 7 to 9 hours of sleep every night, we are not making the most of the monophasic cycle. It promotes deeper sleep cycles and, as a result, higher-quality sleep. Monophasic sleepers may be more able to acclimatize to time zone shifts. On the other hand, people who require more sleep might not receive enough sleep at night, which could lead to sleep deprivation and daytime drowsiness.

Biphasic sleep: There are two phases of biphasic sleep, also referred to as segmented sleep; a long period and a short phase. Typically, they consist of five hours of sleep at night and one to one and a half hours throughout the day (7). But it can also switch to a different 6-hour sleep schedule at night from the noon nap onward; biphasic sleep can enhance alertness and cognitive function. Overcoming sleep deprivation and problems with maintaining sleep might be beneficial. Because of the midday nap, biphasic sleep has been shown to enhance alertness and cognitive function throughout the day. Perhaps more suited for some people. On the other hand, if you sleep too late or too close to bedtime, it can occasionally interfere with your evening sleep. For those who naturally get afternoon weariness, sleeplessness, or cultural practices that involve siestas, biphasic sleep may be helpful (1). Certain people may be naturally inclined to biphasic sleep. Biphasic sleep may be more practical if your schedule is flexible.

Polyphasic sleep: Many phases make up polyphasic sleep, which is used by those who want to be busy all day long with little need for sleep. During 24 hours, resting for a total of 4 to 6 hours is part of a polyphasic sleep regimen (5). Sustained polyphasic sleep restriction abolishes human growth hormone release and neurophysiological changes (8). There are three main types of polyphasic sleep schedules: Uberman, Dymaxion, and Everyman.

a) Everyman Sleep Schedule

There are three types of the most popular sleep schedules Everyman 1, Everyman 2, and Everyman 3. Everyman 1 follows a biphasic sleep schedule, meaning that he sleeps for six hours every night and naps for twenty minutes throughout the day. It's the most feasible and safest sleep schedule, and a lot of individuals might already be on it. Everyman 2 gets 4 and a half hours of sleep and 2–twenty-minute naps during the day. Everyman 3 gets three hours of sleep every night and 3twenty-minute naps.

b) Uberman's Sleep Schedule

The Uberman schedule calls for six 30-minute naps spaced out over a total of three hours of sleep per day. For the majority of modern people, it is an unpredictable schedule that might result in sleep deprivation and little time for deep, restorative REM sleep (9).

c) DymaxionSleep Pattern:

The Dymaxion sleep pattern adheres to a schedule that emphasizes naps. Consists of four 30-minute naps spread out throughout the day, giving one-two hours of sleep every twenty-four hours. The Dymaxion Sleep Schedule is unreliable and can result in health problems and sleep deprivation, just like the Uberman Sleep Schedule.

 Figure1: this figure shows various kinds of sleep patterns such as monophasic and polyphasic sleep-wake patterns (Dymaxion, Uberman, Everyman). https://the-mattress-company.co.za/2022/10/monophasic-biphasic-polyphasic-sleep/; Dated 2/5/2024.

History of sleep-wake pattern in human 

Tribes are the endogenous people who share different geographical areas and have different cultures and some of them are hunters gathered as example; Hadza tribes, Toba, Gond, etc. Most of the information about the history of human sleep-wake patterns comes from studies of tribal populations and anthropological data. The human sleep pattern in the late eighteenth century and early nineteenth century before the invention of electricity and industrialization. Some of the studies stated that the sleep pattern during this period was biphasic. People usually take their first sleep between 09 to 10 PM for approximately 3 hours then the second sleep after midnight till dawn. After this period presence of electric lights and industrialization brought cultural changes, especially in Europe and the USA. This probably changed the sleep pattern. However, we didn’t find evidence of such biphasic sleep in Indian literature. Presently in many Indian states such as Goa, west Bengal, etc., biphasic sleep includes afternoon sleep for 1 to 2 hours followed by night timesleep.

Studies on primitive tribal communities that still maintain characteristics of the pre-industrial, pre-electricity world could provide valuable insights into the sleep patterns of the past. Gond is one of the largest tribal groups in the world presently found in Indian States like Madhya Pradesh, Maharashtra, Telangana, Andhra Pradesh, Bihar, and Odisha (Britannica, T. Editors of Encyclopaedia (2024, March 19). We were unable to find out any study in sleep pattern in gonds or any other local primitive tribes. Hadza, tribes are Tanzanian indigenous they are known as modern hunter’s gatherers. Studies on sleep patterns in the Hadza tribe revealed delayed sleep onset and short sleep (average 6.25 hours) in the population. They spend lots of time in bed without sleep. In addition, higher nocturnal activity during full moonlight is also reported in the tribe (10). However, they display a strong circadian rhythm (11). Sleep patterns in tribes like Toba/Qom - are also peculiar as they start their sleep after some hours of dusk and wake up early before dawn (12).

Significance of the study of sleep-wake pattern

The circadian rest-activity rhythm may give rise to sleep-wake. There is diversity in sleep patterns among animal groups because animals have developed their sleep patterns to fit into their ecological niches and feeding requirements. The sleep-wake pattern is influenced by the prey-predator relationship and seasonality as some animals hibernate in adverse seasons (13). Animals like bats and foxes (crepuscular) are active in twilight and use lower light intensity for predation (14). Likewise, hunter hunter-gatherer humans also showed biphasic sleep patterns that changed drastically after Industrial Revolution (15). Present human society is supposed to be monophasic with many variations. We are globally competing, struggling for existence, and are parallels facing sleep-related problems, like sleep deprivation, poor performance, poor alertness, insomnia, etc. The majority of problems are due to irregular sleep-wake patterns. The population is going through unavoidable nightlife culture and day-time work-load frequently.  To compensate sleep deprivation people, take short naps during the daytime. Chronic sleep deprivation usually remains undetected and may result in transient or permanent sleep disorder. 

Studies on sleep-wake patterns could reveal undiagnosed sleep-wake irregularities and sleep deprivation in the population. To manage a healthy sleep-wake cycle one should look into the factors affecting sleep-wake schedule. 

Irregular sleep wake pattern and sleep disorders

Sleep problems are frequently accompanied by disturbed sleep-wake rhythms (16). Better sleep quality and an improvement in the disrupted sleep pattern are frequently achieved by treating the sleep disorder.  The researchers propose that irregular sleep patterns are a proxy for circadian disruption, which can have broad adverse effects on physiology and increase the risk of premature mortality (17). Disrupted sleep patterns and sleep disorders can be caused by a variety of reasons, such as drugs, heart disease, chronic pain, mental health illnesses, anxiety, depression, and environmental variables like noise and light pollution (18). In addition, sleep regularity, measured by the consistency of sleep-wake timing, was found to be a stronger predictor of mortality risk than sleep duration. Irregular sleep patterns, including variability in sleep duration and daytime napping, is linked to higher mortality risk (19). Moreover, irregular sleep, even when restricted to weekdays, is also associated with an increased risk of cardiovascular events (20).

Irregular sleep-wake rhythm disorder (ISWRD) commonly observed in traumatic brain injury and mental retardation among elderly neurodegenerative patients is characterised by absence of circadian pattern in the sleep-wake cycle (21). The degenerated neuronal activity of suprachiasmatic nucleus (SCN) neurons, a decrease in the circadian clock's responsiveness to entraining agents like light and activity, and a reduction in exposure to bright light and structured social and physical activity during the day could be associated with ISWRD (22).

Human Sleep cycle and sleep-wake pattern

The sleep/wake cycle is essential for the body's rejuvenation and healing, ensuring optimal functioning. Adequate sleep enables the body to synchronize its circadian rhythms, which facilitate the accumulation of energy reserves for metabolic processes, restructuring of neurons for synaptic function, consolidation of memory, and integration of complex motor systems. The central nervous system (CNS) plays a crucial role in regulating the sleep cycle (23). 

Variation in sleep-wake pattern also depends on the quality of sleep. Sleep time cycle is the most studied ultradian rhythm of 90 minutes periodicity that reflects quality of sleep at night. It consists of two phases’ viz., REM (rapid eye movement) and NREM (Non rapid eye movement) that is the period of deep sleep. NREM can be further divided into four stages.

Wake stage is the lightest stage of sleep, Alpha wave was predominated when individual close their eyes. this sleep stage easily disturbs easily awaking and muscle tone throughout the body relaxed and people in this stage experiences sensation of falling. Individual were drossy and closed their eyes (24). REM sleep stage is characterized by muscle atrophy, bursts of rapid eye movements, and desynchronized brain wave activity is characteristics of REM sleep. During REM slow alpha activity, theta activity (three to seven counts per second), and "sawtooth" wave patterns can be observe. REM gets longer and longer as the sleep episode goes on. First stage of NREM is dominated by theta wave in EEG. Alpha wave replaces with low amplitude mixed frequency (LAMF) activity. This at age last around 1 to 5 minutes. In stage 2 of NREM sleep spindle intermixes with sleep structure, known as k complex’s complex necessary for memory consolidation and declarative memory (25). Stage 3 is the deepest stage of sleep phase in which signal with low frequency and high amplitude. This stage is known as deep sleep and delta sleep. In this stage repair of tissue, regrow organ and strengthen of immune system occur (26). Final, stage 4 is an even deeper sleep where the brain waves further slow and sleepers are very difficult to wake. It's believed that tissue repair occurs during the stage of sleep and that hormones are also released to help with growth (16).

Figure 2: Hyponogram-showing stages of sleep-wake cycle; Periods of awakening, REM Sleep, NREM Sleep (stages 1, 2, 3, and 4).  National Library of Medicine.https://www.ncbi.nlm.nih.gov/books/NBK560713/figure/article-28328.image.f1/

Sleep-wake pattern and Rest activity rhythm

Rest-activity rhythms and sleep-wake patterns are closely related concepts that primarily rely on circadian rhythm. For animals that are diurnal, this rhythm inherently encourages alertness throughout the day and lethargy at night. A more comprehensive term for sleep and wakefulness, rest-activity rhythm also includes intervals of increased and decreased activity during the day. It also covers times when a person is awake but is not actively moving, such when they watch TV or sit. Better physical and mental health is linked to a robust and steady rest activity rhythm that includes clear sleep and activity windows. On the other hand, when this regularity is disturbed, it might result in weariness, difficulty sleeping, and other health concerns. Diagnostic and treatment of sleep problems such as insomnia and delayed sleep-wake phase syndrome can be aided by the analysis of rest-activity (54).

Rest-activity rhythm abnormalities have also been identified in people with certain medical problems, such as neurological diseases or depression. Researching rest-activity rhythm also reveals how our sleep-wake cycles and general levels of activity are affected by things like light exposure, work schedules, and social activities (22).

Sleep-wake pattern and Chronotype

The concept of Morning chronotype, evening chronotype and intermediate chronotype as a human trait, has been extensively studied in various research works (81,69). This characteristic describes a person's behavioral inclination to be more active either later in the day (eveningness) or in the morning (morningness). People who do not fall into one of the two categories are categorized as intermediate types (IT). Research has shown that women who are depressed often become more active in the evenings (84).  Morning types tend to fall asleep earlier and wake up earlier, while evening types experience the reverse (sleeps and wakes during latter hours of the day). Similarly the alertness, work output, and performance of morning types are more during early hours as compared to that in evening types. While chronotype is largely genetic, social pressures and environmental factors like work schedules can influence sleep-wake patterns, sometimes leading to a mismatch between your natural preference and your actual sleep schedule. Living in accordance with your natural chronotype can significantly impact your sleep quality. When sleep-wake schedule aligns with chronotype, it allows your body's natural rhythm to regulate sleep and wakefulness effectively, leading to better sleep quality (29).

On the other hand side fighting your natural chronotype by forcing yourself to sleep and wake up at times that don't suit you can disrupt your circadian rhythm, leading to sleep disturbances, daytime fatigue, and difficulty concentrating (Figure 3). It has been documented that depressed woman tends to shift towards being more active in the evening (29). These changes could be linked to hormonal changes during menstrualcycle; a woman experienced feeling of depression. 

Research suggested that eveningness can have negative effect on cognitive function and mental performance (52).There is a connection between eveningness and  mental disorders, like Schizophrenia, attention deficit, hyperactivity disorders, sleep disorders, and mood disorder are correlated.

a) Sleep pattern, health and quality of life

In recent days, there has been a growing interest in monitoring sleep patterns to better comprehend the relationship between sleep, health, and the development of certain diseases due to lack of adequate rest. Poor sleep quality has been associated with health issues such as depression and psychological stress, which can have a detrimental impact on one's overall well-being. Empirical data indicates a correlation between sleep and cognitive functions, problem-solving abilities, decision-making, and innovative thinking (20). Sufficient rest plays a crucial role in combating infections, regulating metabolism, preventing diabetes, and promoting optimal functioning. Good sleep supports brain performance and mood and can decrease risk for many diseases and disorders, like type 2 diabetes, heart disease, stroke, obesity, and dementia (75). On the other hand poor sleep is associated with risk of diabetes, cardiac disorders, obesity, hormonal dysfunction etc (67). Significant negative effects of irregular sleep patterns include sadness, insomnia, poor work performance, car accidents related to employment, and general low quality of life (8).

b) Sleep-wake pattern, Age, Gender, and socioeconomic conditions 

Gender: The 24-h sleep cycle varies between males and females. Generally females sleep earlier than males. The sleep hormone melatonin tends to surge more strongly in females than in males. Men can fall asleep faster than women. Men spend more time in sleep phases 1 and 2, whereas women often sleep deeper and for longer periods of time. Males spend significantly less time in deep sleep as they get older. Likewise men often have longer REM sleep durations. As compared to older men, older females might have greater REM sleep (80).The sleep patterns between men and women exhibit several key differences. Women tend to have an earlier circadian clock, making them more inclined to fall asleep and wakeup earlier than men (78).

Genderand sex hormone influence sleep pattern (60). In females more case of insomnia, reduced sleep quality, and problem in staying asleep as comared to the male (51). Disturbed sleep quality obserbed in women entering the menopause phase of life. The study found that women tend to have more frequent insomnia symptoms, reduced sleep quality, and difficulty staying asleep compared to men(25).The study on russian University students was done for weekday sleep loss and weekend sleep duration, then it was found that Females as compared to male show various differences in sleep quality and patterns. They report a lower subjective sleep quality score, higher morning sleep ability score, and lower night-time and daytime wake ability scores. Additionally, females, more frequently experience excessive daytime sleepiness and being sleepier at any time of the day, with the most significant male-female difference observed around sleep onset and offset times (72). On free days, female report longer sleep duration and an earlier sleep onset, with a larger difference in sleep duration between free days and weekdays (72). Women indeed tend to fall asleep and wake earlier than men by about 2 hours, resulting in a nearly half-hour earlier secretion of melatonin occur.

In different studies it was found that sex hormone such as progesterone and esterogen in women play a significant role in regulating sleep quality and stage through the different phase of Menstrual cycle (38). The menstrual cycle is connected to changes in circadian rhythms and sleep patterns, leading to decreased sleep quality and more disruptions in sleep for women during the premenstrual week (64).

Age: Sleep physiology changes with age. In elderly people amplitude of circadian rhythm as well as melatonin and cotisol level of hormone decreases with age. Increase in sleep latency, fragmented sleep and wake bouts are common among elderly subjects. Likewise decreased sleep efficiency, sleep duration and deep sleep is prominent in elderly as compared to their younger counterparts.

Socio-economic factors: socioeconomic condition and sleep is complex and involved a combination of physical and mental stress and health disparities such as diabetes, obesity, cardiovascular disorders etc (69). There's a clear and well-established link between socioeconomic conditions and sleep-wake patterns. Individuals with lower socioeconomic status often experience poorer sleep quality compared to those with higher socioeconomic status. Lower socioeconomic status individuals with lower income, education levels, or occupational status tend to sleep less, insomnia, sleep apnea, restless leg syndrome etc., as compared to that in individual with higher socioeconomic status. This can be attributed to various factors like, shift work, stress and anxiety, Poor quality housing may lack proper temperature control, light pollution, or noise disturbances, hindering sleep quality, higher rates of sleep disturbances (40)

c) Sleep pattern, geographical and environmental factors

Moonlight: moonlight is found to be associated with reduced sleep duration, later sleep onset and increased wakefulness. Studies have shown that people may sleep slightly less during the nights leading up to a full moon, when the moon is brightest. This could be due to the increased moonlight disrupting melatonin production, a hormone that regulates sleep (14). However, the impact is relatively smaller with inter individual differences. In addition, factors like artificial light, sleep habits and environmental factors are confounding the effects of moonlight. 

Impact of Moonlight to change earth electromagnetic field and Moon gravitational pull affect sleep wake cycle (46). Various studies have done that effect of lunar phase on biological rhythm. The mechanism by which photoreceptor used to detect Moon light and entrained the endogenous clock (46).

Sunlight: sunlight is essential for controlling our circadian rhythm, which in turn controls our sleep-wake cycles (53). It serves as an external time cue, or zeitgeber, to synchronise the circadian cycle. A hormone that encourages sleepiness called melatonin is suppressed when exposed to sunlight. Melatonin production rises with dusk, promoting sleep and tiredness. It encourages an early bedtime and improved sleep quality at night, which in turn results in a regular sleep-wake cycle, increased energy during the day, and attentiveness.Exposure to artificial light at night can disrupt circadian rhythms and is associated with an increased incidence of mood disorders, metabolic dysfunction, and certain cancers .Humans residing in dark and temperature-controlled caves persist in exhibiting circadian sleep-wake patterns and maintaining body temperature rhythms, albeit with a slightly longer than 24-hour cycle when left to their own devices.

Seasonality: Seasonality can indeed influence sleep patterns in several ways. Longer daylight hours during summers can lead to later sleep onset and potentially shorter sleep duration. This is because increased light exposure suppresses melatonin production, the sleep hormone. Shorter daylight hours and decreased sunlight exposure in winters can lead to earlier sleep onset, and in some cases, individuals may even experience increased sleep duration. During summers hot and humid nights can make it difficult to fall asleep and stay asleep, leading to sleep disturbances and decreased sleep quality. Summer brings longer daylight hours, which can suppress the production of melatonin, the sleep hormone. This delayed melatonin release makes it harder to fall asleep at night, leading to sleepiness during the day and an increased desire for naps (65). The body works harder to maintain its internal temperature during hot weather. This extra energy expenditure can leave you feeling drained and more prone to daytime sleepiness (32). On the other hand side winters are cooler and can promote deeper and more restful sleep, potentially leading to better sleep quality (65). Sleep duration may be slightly longer compared to other seasons. However in some individual’s seasonal Affective Disorder (SAD) a type of seasonal depression increased sleepiness and a desire for more sleep (2).During the spring season, wake times tend to be earlier, and sleep duration decreases compared to the reference season of winter. This shift in sleep patterns may be influenced by the changing daylight exposure and temperature conditions (56).Overall, the body's natural sleep-wake cycle can fluctuate throughout the year in response to seasonal changes in light exposure, temperature, and environmental cues. These variations can influence the timing of sleep onset, wake times, and overall sleep quality, highlighting the importance of maintaining a consistent sleep routine to support optimal rest and well-being reliance on circadian behavioural rhythmicity in environments with weak light-dark cycle.

Latitude: Latitude is correlated with morningness-eveningness (M/E) preferences, with higher latitudes generally associated with a more evening-oriented circadian rhythm. This means people living at higher latitudes tend to have a later sleep-wake cycle compared to those closer to the equator (55).Longer photoperiods (daylight hours) at higher latitudes are associated with a more evening-oriented chronotype(55).The inter-individual differences in sleep-wake behaviour also tends to increase with distance from the equator, suggesting the circadian system may be more stable closer to the equator where light-dark cycles are more consistent(55) . Latitudinal clines have been observed in the amplitude, phase, and period of circadian rhythms in some animal species like fruit flies, with decreasing circadian amplitude and advancing phase as latitude increases (39)

 Sunlight exposure plays a crucial role in regulating our circadian rhythm, the internal clock that governs sleep-wake cycles. Conversely, those residing at higher latitudes experience greater seasonal changes in daylight, potentially leading to adjustments in sleep and wake times across seasons (61).Research suggests that individuals at high latitudes, where daylight can be extended during certain seasons or limited during others, may exhibit unique adaptations in their circadian rhythms. 

Environmental Factors: Extreme temperatures can disrupt sleep quality. Hot and humid environments can make falling asleep and staying asleep difficult. Here are some specific examples of how geographical conditions can influence sleep patterns. Scandinavian countries, individuals living in high-latitude regions like Scandinavia tend to have later bedtimes and shorter sleep durations during the summer months due to the extended daylight hours due to their northerly location, experience significant seasonal variations in daylight (56). Mediterranean cultures often embrace a "siesta" pattern, with a shorter sleep period of around 5 hours at night and a 2-3 hour nap or rest period in the afternoon.

Cultural Factors: Different cultures have varying attitudes towards sleep and daily routines. Some cultures prioritize late nights and socializing, potentially leading to later sleep times.Cultural factors, including cultural values, beliefs, and practices, can significantly influence and shape sleep patterns, particularly in young populations (41). Numerous sociocultural and behavioral elements are linked to a higher risk of cardiometabolic diseases, such as lower socioeconomic status, poor dietary habits, and inactive lifestyles. Another contributing factor to the increased risk of cardiometabolic diseases is inadequate sleep (44).

Work schedules: Work hours and societal expectations can influence sleep schedules. Countries with strong work cultures might have later average sleep times compared to those with a more relaxed approach. The relationship between work schedules and sleep quality is well-documented in various studies. Research has shown that factors like shift work, night shifts, and job stress can significantly impact sleep patterns and lead to sleep deprivation (19).

Light pollution: Exposure to artificial light at night can disrupt the circadian rhythm and lead to sleep disturbances. Cities with high levels of light pollution might experience higher rates of sleep problems compared to rural areas (67).Light pollution has been found to negatively impact on sleep quality and duration as well as hormonal imbalance (44). Studies have consistently shown that exposure to artificial light at night can disrupt the body's natural sleep-wake cycle, leading to reduced sleep quality and duration. This disruption is primarily caused by the suppression of melatonin, by the artificial light (73).

Tools and techniques to study Sleep-wake pattern

All the tools and techniques used to study the sleep wake pattern are non-invasive and human affable.

Polysomnography (PSG): It is regarded as the "gold standard" for sleep investigations. It monitors heart rate, breathing patterns, muscle activity, eye movements, brain activity, and respiratory patterns as you sleep using a variety of sensors. It offers the most comprehensive details on suspected sleep disorders, sleep disruptions, and sleep stages. It is usually carried out in a sleep lab.

Actigraphy: It is a wrist-worn gadget that tracks movement and exposure to light. It potentially detects rest-activity rhythm in free living situations. It offers information on sleep duration, patterns of sleep and wakefulness, and sleep disruptions. Long-term monitoring in natural environments is possible thanks to this less invasive and more practical option than PSG. The accuracy of identifying sleep stages may be marginally less than that of PSG.

Sleep Diaries: These are the self-reported sleeps and wake periods, sleep duration, and functioning during the day. Provide a personal opinion regarding sleep habits and possible sleep problems. It is affordable and simple to use, but it is subject to recall bias.

Light meters: Track your exposure to light, which might affect your sleep-wake cycles. 

Questionnaires: Standardized questionnaires are used to evaluate suspected sleep problems, daytime drowsiness, and the quality of sleep. 

Mobile apps: While accuracy may vary, several apps employ smartphone sensors (such as the accelerometer and microphone) to approximate sleep habits.

The particular research issue or clinical necessity will determine which assay is best. For a thorough examination of the phases of sleep and possible problems, PSG is recommended. Actigraphy is frequently employed for long-term sleep pattern tracking in natural environments. Sleep diaries are useful for the subjective evaluation of sleep quality and daily functioning. Mobile apps and questionnaires are helpful resources for determining whether a person may have sleep issues. It's crucial to remember that no assay is ideal, and combining techniques might give a more complete picture of a person's sleep-wake cycles.

Sleep problems may become one of the most common problems worldwide. Study of sleep-wake patterns of human society is one of the potential areas of future research. Examining how artificial light exposure affects circadian rhythms and sleep patterns over time may lead to the creation of lighting regulations and other measures to lessen the adverse effects. As shift work becomes more prevalent in today's world, measures to maximize sleep schedules and reduce health hazards related to it must be developed. More research into the reciprocal relationship between sleep and mental health issues like anxiety and depression could result in more efficient treatment plans. Furthermore, studies could concentrate on the long-term effects of persistent sleep deprivation on health. The possible advantages of napping and how it affects performance and cognitive function. The social and cultural elements that affect how people sleep in various demographics. Through further exploration of these domains, scholars want to acquire an all-encompassing comprehension of human circadian rhythms and devise tactics to foster ideal sleep well-being for both individuals and the community at large.

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