What Is Sleep

Verified by World Mental Healthcare Association

Sleep is an important biological process that helps us to stay healthy, process information, and feel rested. By understanding what is sleep, we can avail of the physical and mental health benefits that come with quality sleep.

What Is Sleep?

Sleep is defined as a naturally recurring state of mind and body, characterized by unconsciousness yet active brain- and body- functioning. It is often distinguished from other similar conditions like wakefulness and disorders of consciousness. Sleep is an altered state of consciousness that involves lower muscle activity, limited sensory activity, and fewer interactions with the environment. This state is marked by lower awareness of the surrounding and environmental stimuli. It is a repetitive process where we react less to external or internal stimuli but includes active brain patterns.

This physiological behavior is observed in all species of animals with humans spending almost one-third of their lives sleeping. Although researchers are yet to determine the exact function of sleep, it is believed that this physical and mental process is crucial for our survival. Sleep deprivation for a long period of time can lead to physical and cognitive impairment and may also prove fatal. However, sleep is separate from hibernation, coma and death.

A 2021 study 1 elaborate the understanding of what is sleep as “a complex physiological process [and brain patterns] in which the body and the mind go into a rest state for some time”. It occurs in multiple stages and involves multiple complex physiological processes and brain activity, despite the reduction in interactions between the body and outside stimuli. It often synchronizes with our circadian clocks, bodily needs, and environmental factors like light, temperature, etc.

Understanding Sleep

The Benefits of Sound Sleep

Most research uses the complementary categories set forth by the esteemed Dutch biologist, Nikolaas Tinbergen 2, to describe typical characteristics of animal behaviors like sleep. These include:

1. Function

Sleep plays a significant role in metabolic regulation, energy restoration, boosting immunity, detoxification, brain maturation, tissue regeneration, synaptic optimization, etc.

2. Phylogeny

Sleep exists in all higher and lower life forms, including vertebrates, invertebrates, birds, etc.

3. Mechanisms

Certain mechanisms (like genes, neurotransmitters, neural structures, and the circadian clock) influence the sleep-wake systems in all organisms.

4. Ontogeny

Sleep manifests itself differently in different species, depending on sleep duration, sex differences, activity differences, etc.

Sleep is one of the most conserved behaviors 3 throughout human evolution, humans roughly spent over one-third of their time sleeping. It is necessary that they receive adequate and quality amounts of sleep for their survival—just like water, air, and food—as sleep deprivation often comes with severe consequences on a person’s mental and physical health and social functioning 4.

Experts recommend a well-balanced schedule of quality sleep and rest, good nutrition, and adequate exercise for a heart-healthy lifestyle.

What Happens During Sleep?

Sleep is a fundamental parcel of the two-process sleep-wake system that gets a person through his/her day-to-day life. According to one 2006 study 5, “the sleep-wake system is thought to be regulated by the interplay of two major processes, [namely], one that promotes sleep (process S) and one that maintains wakefulness (process C)”:

A. Process S

It is the homeostatic drive for sleep. It accumulates throughout the day, peaks in the hours before bedtime, and dissipates across the nocturnal sleep cycle.

B. Process C

It synchronizes with the circadian clock and environmental light-dark cycles to promote wakefulness and alertness. It declines at bedtime to consolidate the sleep drive and increases as the sleep cycle progresses towards wakefulness.

Both the processes are regulated by signals from different organs of the body, neuronal activity 6 in the brain, chemical secretions (like serotonin, norepinephrine, and adenosine) and the body’s own thermoregulation. Throughout the sleep wake-cycle, certain physiological changes also occur in the body, including:

  • Changes in blood pressure and heart rate
  • Decreased sympathetic nerve-activity
  • Faster and more erratic respiratory changes
  • Reductions in blood flow and metabolism
  • Changes in the renal blood flow and urine flow
  • Changed hormonal secretions
  • Enhanced functioning of the endocrine system

What Are The Different Stages Of Sleep?

According to one 2021 study 7, the sleep cycle is divided into 5 stages consisting of both rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. However, organizations like the American Academy of Sleep Medicine (AASM) and others have their own classification of the sleep stages. The human body usually cycles through these stages 4–6 times, but as the depth of sleep increases “fewer NREM stages occur and the duration of the REM sleep episodes increases”.

The different phases of sleep involve:

1. Wake (Stage W)

The wake stage or stage W occurs in states of eye-open wakefulness and drowsiness, involving eye movements that are associated with wakefulness. It is associated with both alpha and beta waves.

2. N1 (Stage 1)

The N1 stage is the first and lightest stage of sleep, involving low-amplitude mixed-frequency (LAMF) activity, regular breathing patterns, reduced eye movement, and relaxed skeletal muscles. It makes for 5% of the total sleep cycle.

3. N2 (Stage 2)

The N2 is the second and comparatively deeper sleep stage that involves a drop in heart rate and body temperature and the presence of sleep spindles and K-complexes. This stage is associated with long delta waves and it makes up about 50% of the total sleep cycle. As such, the majority of a person’s sleeping time is spent in the N2 stage.

4. N3 (Stage 3)

N3 is the deepest stage of slow delta-wave sleep, wherein the body repairs itself by regrowing its tissues, building bones and muscles, and strengthening the immune system. This stage makes up 10–14% of the sleep cycle and is associated with mental fogginess and temporarily impaired mental performance.

5. REM Sleep

The low-voltage, mixed-frequency stage of REM sleep is associated with dreaming, relaxed skeletal muscles, erratic and irregular breathing patterns, and bursts of rapid eye movements. It is usually linked to essential cognitive functions like learning, memory, and creativity. Each of the REM cycles deepens with the duration of sleep, sometimes lasting up to an hour at a time.

Read More About REM Sleep Here

Why Do We Sleep?

Sleep is an essential bodily function that allows us to recharge 8 our bodies and minds and feel refreshed when we wake up. According to a 2007 study 9, “sleep is considered to be important to body restitution, like energy conservation, thermoregulation, and tissue recovery”. It also boosts cognitive performance and improves moods.

Problems Caused By Inadequate Sleep

Research 10 also shows that sleep loss has serious implications on one’s health, especially when it comes to:

  • High blood pressure
  • Cardiovascular diseases
  • Immunological changes
  • Metabolic complications (leading to obesity or weight loss)
  • Behavioral changes
  • Structural and functional changes in the brain
  • Somatic problems
  • Mental disorders (like anxiety, depression, etc.)

Read More About Anxiety Here

Therefore, the importance of getting enough sleep lies in its benefits related to a person’s mental and physical health and quality of life. How much sleep do we really need varies considerably according to our individual age, needs, and functioning? The medical recommendations 11 for sleep length variously include:

  • 7-8.5 hours for adults
  • Up to 16 hours for babies
  • At least 12 hours for toddlers
  • At least 9 hours for teenagers
  • More than 9 hours for pregnant women
  • Over 9 hours for people recovering from illnesses and surgeries

What Is Sleep Deprivation?

The internal mechanisms 12 of the homeostasis process and the circadian rhythm influence our sleep drive during the ceaseless cycles of sleep and wakefulness. However, a wide array of both internal and external factors can dramatically alter our sleep-wake systems and lead to what affects sleep quality, namely, sleep disruptions and sleep deprivation.

One 2007 study collectively refers to sleep disruptions as “sleep problems that impact the continuity of sleep”. Sleep deprivation or sleep loss 13, on the other hand, involves a person experiencing deficits in quantity and quality of sleep owing to factors.

According to research, a person’s sleeping pattern and schedule are determined by factors such as:

  • Stressful and fast-paced lifestyles
  • Alcohol consumption
  • Consumption of caffeine
  • Consumption of tobacco and recreational drugs
  • Medications, like antidepressants and diet pills
  • Temperature differences and nocturnal body movements 14
  • Presence of chronic illnesses
  • Sleep disorders (like 15 insomnia, narcolepsy, sleep apnea, restless leg syndrome (RLS), etc.)

Read More About Insomnia Here

Tips To Sleep Better At Night

With prolonged wakefulness being a widespread phenomenon, epidemiologic and experimental research 16 suggests individual sleep hygiene recommendations 17 to improve a person’s quality and quantity of sleep.

Tips To Achieve Quality Sleep

Consider the following tips to sleep better at night:

  1. Establish a realistic sleep schedule and maintain this sleep timing regularity every night
  2. Maintain low light levels and comfortable temperature settings in your bedroom
  3. Create a comfortable sleeping environment with mattresses, pillows, curtains, rugs, etc.
  4. Maintain a data sheet for your body type, sleep preferences, and the best sleep positions
  5. Limit your “screen time” before bedtime
  6. Abstain from large meals and consumption of alcohol or caffeine in the hours leading to bedtime
  7. Avoid consumption of tobacco, nicotine, etc.
  8. Consider including in your diet the food items that enhance sleep, such as nuts, rice, milk, fatty fish, tea, etc.
  9. Get adequate physical exercise throughout the day
  10. Consider activities like sex, cold shower, massages, etc. that enhance sleep
  11. Abstain from daytime napping and resort to “power naps”, if necessary
  12. Avail therapy, stress management strategies, ASMR techniques, etc. to address sleep problems

Read More About Stress Here


Adequate and high-quality sleep is an important cornerstone of human health, behavior, and functioning. By understanding what is sleep and how we can improve it, we can avail ourselves of the benefits of a balanced lifestyle that comes with a sound sleeping schedule, good nutrition, and adequate physical activity.

Sleep At A Glance

  1. Sleep is a periodically occurring state of mind and body involving unconsciousness yet active brain- and body- functioning.
  2. There are 5 different phases of sleep.
  3. Both the homeostasis process and the circadian rhythm influence our sleep drive.
  4. Sleep disruptions and sleep deprivation cause a number of physical and mental health problems.
  5. Quality sleep and its benefits can be achieved by following a healthy sleep hygiene routine.

Frequently Asked Questions (FAQs)

1. What Is the Best Temperature for Sleep?

The best temperature for sleep is approximately 65 degrees Fahrenheit or 18.3 degrees Celsius.

2. How Long Should I Nap?

Studies show that the best nap length to prevent drowsiness is between 10 to 20 minutes. However, “power naps” lasting for about 45 minutes is linked to enhanced memory and cognition.

3. What Is Sleep Hygiene?

“Sleep hygiene” refers to healthy habits, behavioral patterns, and environmental factors that enable good quality and uninterrupted sleep.

4. What Is REM Sleep?

REM sleep involves that stage of sleep in which a person has dreams and experiences random rapid movement of the eyes and low muscle tone throughout the body. It is also known as paradoxical sleep (PS) or desynchronized sleep.

👇 References:
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