Sleep Cycle and Stages


Sleeping is a critical part of every person’s life. We spend approximately one-third of our life asleep. Yet, most people don’t fully appreciate just how important sleep is to living a healthy life. The need to sleep is as important as the need to eat and breathe.

Sleep is a mental and physical resting state in which a person becomes unaware of the environment and is seemingly inactive. Essentially, sleep is a detachment from the world, wherein most external stimuli are blocked from the senses. Despite the apparent inactivity there are vital functions that are performed during a normal sleep pattern.

Sleep is a required activity. It is not optional. It is not something that you just do when you are inactive. Sleep is important for normal cognitive and motor functions, it is vital to proper functioning and overall health.


Many of us feel that sleep is a waste of time. There are far better things to do after all. As an additional dismissal of the importance of sleep, our society praises the workaholic CEO who claims that he or she only needs five hours of sleep a night. How often we hear people say things like “I like to work hard and play hard” or “I’ll sleep when I’m dead.”

Despite these beliefs and societal pressures, sleep is essential. It is a time of rejuvenation and rest, and it benefits us in several ways. How well you function the next day is directly contingent on how much you slept and, more importantly, how well you’ve slept.

When we sleep, our bodies produce hormones. Human growth hormones, HGH, help to build and repair muscle mass, tissue and cells. Melatonin, a hormone that is released during the onset and duration of sleep until around 2 am or 3 am helps us fight infections. These critical biological functions help us understand the importance of a good night’s sleep in helping to keep us healthy and well. Sleep has a direct impact on our:

Productivity & Concentration:

The quality of sleep that we’ve had the previous night determines our productivity for the next day. When we sleep, we clear our heads and we are able to think more clearly and better recall what we learned the day before. With a good night’s sleep, we are able to focus better and react quickly to the day’s challenges. Lack of sleep makes us drowsy, slows our response time and lowers our overall productivity.

Health & Energy:

For good physical and mental health, adequate sleep is crucial. Research and studies have shown that those who do not get enough sleep are more prone to illnesses and show accelerated signs of aging. Moreover, not being able to get a good night’s rest may be a sign of a sleep disorder or other condition that may be affecting your health.


Sleep affects our disposition. Lack of sleep makes us ill-tempered. Additionally, people who are constantly sleep deprived are more prone to depression. Getting the right amount of sleep enables us to have a positive outlook on life.


A basic understanding of the sleep stages and the sleep cycle can enable us to better understand what sleep does for us. Sleep is regulated by our internal body clock, time of day, light stimulus and various other factors. As we sleep, we pass through different stages and states of sleep, which are only fully experienced with continuous, uninterrupted sleep. We need to go through all of these sleep stages to have healthy sleep. There are two main types of sleep:

Dream Sleep: REM Sleep, Rapid Eye Movement

REM sleep is when we do most active dreaming. Our eyes move back and forth quickly, giving this stage of the sleep cycle the name REM sleep. REM sleep is also referred to as dream sleep. Research has shown that REM sleep functions to reinforce what we have experienced and learned the day before.

We enter into REM sleep around 70 to 90 minutes into our sleep cycle. Generally, we have three to five REM cycles each night. Our brain becomes active, heart rate and breathing become irregular and the blood pressure also rises.

Dream sleep is important to our minds for consolidating and processing memories and emotions. Most of the dreaming occurs during this time, though researchers believe a small percentage of dreaming could happen during the other stages as well.

During dream sleep, some of the ability to regulate body temperature is lost, therefore, extremely hot or cold temperatures in the environment can interrupt sleep. If our REM sleep is interrupted one night, our body tries to catch up and make up for the REM sleep lost the previous night by increasing the length of the REM sleep cycle the next night.

NREM Sleep, Non-Rapid Eye Movement Sleep

NREM is made up of four different stages of sleep. Stage 1 and 2 are called light sleep. Stages 3 and 4 are called slow wave sleep.

Light Sleep: Stages 1&2 – During stage 1 of sleep, we drift in and out of sleep. It lasts for around a few minutes, and we are awakened easily during this stage. Muscle activity slows down during this stage, and our eyes move slowly. Those who are awakened at this stage of sleep often recall fragmented visual images. In stage 2, heart rate slows, eye movements stop and body temperature drops.

Slow Wave Sleep: Stages 3 & 4 – The first stage of slow sleep typically lasts two hours. Breathing slows down, and we regain energy. Hormones are released to rejuvenate our bodies. There is a decrease in blood flow to the brain, which is redirected towards restoring physical energy. The immune system is activated to fight disease and restore health.

It is difficult to awaken anyone during this stage of sleep, and if awakened, people feel rather disoriented for a few minutes. Research has shown that if the amount of sleep we are getting is reduced, the unconscious mind prioritizes slow wave sleep the next time we fall asleep.

Circadian Rhythm

Normal changes in the physical and mental characteristics that take place during the day are known as circadian rhythms. The body’s biological clock controls most circadian rhythms. This clock is known medically as the SCN, or suprachiasmatic nucleus, and is located in the brain in the hypothalamus. The SCN is two brain structures that are about the size of a pinhead and they are located near the nerve center that processes information from the retina.

The SCN receives signals through the eyes. Signals from the SCN are then transported to different areas of the brain, such as the pineal gland. This gland responds to light-inducing signals and regulates the production of the melatonin hormone. When it’s dark, the level of melatonin in our body increases, which in turn makes people feel sleepy.

Various other functions are coordinated with the sleep/wake cycle. Some of these include hormone secretion, body temperature, blood pressure changes and production of urine.

The circadian rhythm can be reset by bright lights or sunlight, and therefore our biological cycles, rather than our innate cycle, follow the cycle of the sun. To a certain degree, circadian rhythms are also affected by external time cues such as the ringing of an alarm clock, meal timings, a bed-time ritual etc.

The circadian rhythms of those who move from one time zone to another are disrupted, and they experience what is commonly known as jet lag. It generally takes a few days before our body cycles get adjusted to any new sleep schedule.


Sleep needs change throughout our lifecycle and vary from person to person. Several factors such as genetics, age and gender are crucial in determining the amount of sleep that we need. For most people a good rule of thumb is seven to eight hours.

It is not just the amount of sleep that we get but the quality of sleep is what is important. When you are sleeping soundly and waking up feeling rested and restored that is the amount of sleep that you need on a regular basis.

  • Newborns – sleep between 16 and 18 hours a day
  • Preschool children – sleep between 10 to 12 hours a day
  • Teens and school-aged children – need around 9 to 11 hours of sleep
  • Adults – require around 7 to 8 hours of sleep each night.

While most people need 7 to 8 hours of sleep per night, others may need more or less depending on personal factors. Importantly, the required hours of sleep are for active sleep and it does not include time spent in bed trying to get to sleep. Whatever amount of sleep you need, what is important is that you wake up feeling refreshed and rested.

Many people believe that as we get older, we need less sleep. However, there is no evidence to confirm this. Researchers believe that older people sleep less due to increased sleep disrupters such as physical ailments or a lack of exercise, not because they need less sleep. This is why older people may only sleep 6 or 7 hours a night but supplement their sleep with an afternoon nap.


When we get too little sleep, it literally shows on our faces. We have bags under our eyes and are just plain tired-looking. These symptoms are just the tip of the iceberg when it comes to the effects that too little sleep has on our bodies, and our minds.

Sleep deprivation can cause many strange effects on the brain, adversely effecting cognitive functions. For instance, those who do not get enough sleep often find it difficult to perform the simplest of tasks and have difficulty remembering things. There is a link between sleep deprivation and many psychological disorders, including depression.

Some of the more common effects of too little sleep include irritability, memory loss, high blood pressure, headaches and muscle aches. A lack of sleep can also cause a number of physical problems, including overall fatigue, and it can even lead to serious health conditions, including hypertension and diabetes.


Unfortunately, many of us do not get nearly enough sleep. Sleep deprivation can, over time, affect our overall health, both physical and psychological. There are many reasons why people don’t get enough sleep, including just simply staying up too late or taking too long to fall asleep and then getting up at the normal time.

Some people may have difficulty falling asleep, others staying asleep and others wake up too early. Depending on when the sleeping difficulty occurs the causes of the problem may differ. An accumulation of sleep deprivation is known as sleep debt.

Factors That Can Lead to a Lack of Sleep

Caffeine – This is a stimulant, and one that keeps people awake. It is recommended that to get a good night’s sleep, people should avoid food or drinks containing caffeine in the afternoon and later in the evening.

Age – Even age can affect how people sleep. For instance, as we age we do not sleep for nearly as many hours we they did when we were younger. This can affect health adversely as the amount of sleep that we need does not usually change during our adult lives. With age it can become more and more difficult to get to sleep at night and to stay asleep.

Diet – Often, the reason that many people have trouble sleeping is because they are not getting all of the proper vitamins and nutrients needed every day or that what they are eating and drinking is acting to disrupt sleep. Many people are snacking at night, which can disrupt sleep if the body is still trying to digest the food.

Drugs – If you have been recently prescribed medication by your doctor, and also had difficulty sleeping, there is a strong possibility that is the cause of the sleep disruption. Many medicines can cause insomnia, check with your doctor or pharmacist to evaluate the side effects of the medication.

Alcohol – Many people often turn to alcohol if they have had trouble sleeping. While alcohol does help you fall asleep it may impair your ability to stay asleep. It is a diuretic and may wake you up to urinate or drink water. Turning to alcohol to help you sleep can lead to dependency and potentially addiction.

Smoking – Nicotine is a stimulant, smoking just before going to bed will keep you up. Additionally, if you are addicted to nicotine, your body may wake you up in the middle of the night with withdrawal symptoms.

Physical Problems – There are numerous physical problems that can lead to sleep disorders. For instance, those who are suffering from any type of aches or pains may find themselves unable to sleep due to their discomfort. Many illnesses can also cause sleep deprivation.

Genetics – It has been discovered that there are important genes that can affect sleep patterns, these genes have an effect on how much sleep we need. Often, if one family member has difficulties sleeping or requires more or less sleep than average, there are other family members with the same trait.

Environmental Factors – For optimal sleep, it is recommended that people sleep in an area that is dark and free of noise. While people can adapt to an environment with noise, sudden noises above that level can disrupt sleep. Also, many people cannot sleep in a cluttered area. If there are smokers in the home, this can cause sleeping problems due to poor breathing, and other pollutants that cause allergies can also be a factor in not getting proper sleep.

Sleep Disorders – There are a number of sleep disorders that can severely impact normal sleeping patterns. These disorders can range from mild (insomnia) to serious (sleep apnea). If you are having an extended period of sleep deprivation review your symptoms with your doctor to better understand if you have a sleeping disorder or if the symptoms indicate another condition.


A vital biological function, sleep is not a waste of time. It is important to a person’s emotional and physical well-being. Various sleep studies have shown that not getting the required amount of sleep can drastically affect a person’s ability to perform even basic functions. There are two primary theories of why we need sleep:

Restorative Theory

This theory holds that our mind and body are re-energized, rejuvenated and restored with sleep. The core of this theory is that sleep functions to restore what is lost or depleted when we are awake. When a person sleeps, the brain performs some important tasks, such as integrating new information, organizing memory and the body repairs nerve cells and tissues.

Adaptive Theory

The adaptive theory holds that sleep is an evolutionary adaption that kept us out of the way of predators while our vulnerability was the highest – night time. This theory believes that sleep may have evolved as an adaptive and protective function. We searched for food during the day and hid in the night for protection.

While the answer to the question on why we need to sleep has not been definitively answered by researchers we can clearly recognize the importance of sleep through our knowledge of what happens when to us when we don’t sleep.

Essential further reading:

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