How sleep phases affect human health and what is the secret to good sleep

Most people only know in general terms about what phases of sleep exist and what happens in the body after we close our eyes. Moreover, each phase is important and has an impact on the quality of rest, and human health in general.

Sleep phases are temporal and functional segments into which sleep has been divided by researchers. By and large, an ordinary person who exists in the “wheel” of life does not care whether these phases exist or not.

However, sleep functions directly affect the state of the human body. This is both health and longevity. It is because of the importance of the quality of sleep that a lot of money is invested in sleep research by world medicine.

Sleep is an unusual state of the body that is sometimes compared to death. In fact, they have little in common. In contrast to the complete death of the body, rest, on the contrary, contributes to a long life. It renews all systems, helps to restore physical and moral strength.

At the same time, sleep is not something homogeneous in structure. There are different phases of sleep, each of which performs a specific function and lasts a very specific amount of time. Everyone knows deep sleep is good for you. But when it comes, how it affects the body – only a few know about it.

Sleep functions

While awake, people and animals spend a lot of energy. Sleep is one of the body’s self-regulation mechanisms that helps restore this energy. Its main functions are as follows:

  • rest of the nervous system;
  • restoration of physical strength;
  • “Rebooting” of the brain (at night the information received during the day is processed, systematized and stored);
  • cleansing the body of toxic substances (it is not for nothing that doctors recommend that sick people sleep more);
  • restoration of immunity;
  • cell renewal;
  • the ability to usefully for the body to wait out the period of darkness.

Prolonged deep sleep helps to improve memory, burn excess fat, overcome stress and illness.  

What is the functional difference between the phases of deep and REM sleep? 

During different phases, information is processed differently in the brain. REM and slow sleep help to remember the events that have occurred, plan your future, but each in its own way.   

The phase of slow sleep “turns on” memory resources. When a person falls into a deep sleep (aka slow), all the information received during the day begins to be systematized and “put on the shelves.” This phase improves memorization, logical thinking.   

REM sleep is a real “workshop” of the future. With its help, the brain models possible scenarios for the expected events. No wonder they say that they had a “prophetic” dream. By itself, of course, it is not prophetic. It’s just that during the period of REM sleep, a person has models of the future, one of which, when he wakes up, he has realized. All this happens on a subconscious or intuitive level. However, a person’s rest is not limited to these two phases . It has a more complex structure.        

Phases and stages

There are 4 main stages of sleep:

  1. Falling asleep.
  2. Slow sleep.
  3. Fast.
  4. Awakening.

Each phase is characterized by a certain duration and accompanying only physiological processes.

Falling asleep

1st phase – falling asleep. While a person falls asleep, the sensitivity of the sensory systems and heart rate decrease, and consciousness gradually “turns off”. Even the glands begin to work less actively. This can be noticed by burning eyes, dryness of the oral mucosa. The approaching phase of falling asleep can be easily identified by obsessive yawning.

Such sensations are often noticed by night owls who stayed up late reading or watching TV. If all the described signs are present, it is time to give the body a rest. The falling asleep phase is the shortest. It usually lasts about 10 minutes. Then slow sleep begins , which, in turn, is divided into several stages. 

What is slow sleep 

Rest is called slow, in which brain activity remains in a low-amplitude range. Scientists record this using an EEG (electroencephalogram).  

All phases of a person’s sleep take different durations in time . If 10 minutes is enough for falling asleep, then the phase of slow sleep takes from 80 minutes to 1.5 hours. The duration depends on the individual characteristics of a person’s physiology, as well as on his mode of rest. Unlike REM sleep, the REM sleep phase is divided into several stages.        


Slow-wave (aka slow) sleep has the most complex structure. It is divided into 3 phases (or cycles):   

Light sleep phase

It begins immediately after falling asleep and lasts about half of the slow time. At this stage, the muscles of a person completely relax, breathing becomes calm, deep. The body temperature drops slightly, the heart rate slows down. The brain completely goes into rest mode.

The EEG records sleepy spindles at this time. So scientists called theta waves, folding in a sigma rhythm (12-14-20 Hz). Such work of the brain indicates a complete shutdown of consciousness.

A person’s eyes do not move at this time. He is completely relaxed, but does not sleep very deeply yet. It is easy to wake up a person during light sleep. Loud sounds or physical stimuli can return him to a state of wakefulness.

Slow sleep phase

At this time, brain activity is expressed in the production of delta waves, the frequency of which is equal to 2 Hz. This is the quietest and slowest mode.

It takes about half an hour in duration. In this phase of slow wave sleep, a person sometimes has dreams.

Deep sleep phase

At this time, the person sleeps deeply and soundly. The EEG is dominated by delta-wave oscillations with a frequency of 2 Hz. The slow and deep phases are often collectively referred to as delta-wave sleep. The duration of the deep sleep phase takes up approximately 15% of the entire night’s rest.    

The duration and characteristics of the deep rest phase have been studied closely by specialists for a long time. It was found that during this time the brain actively produces dreams (about 80% of all visions that a person visit during the night). Dreams appear in the form of pleasant images or nightmares. Most of them, when a person wakes up, forgets.  

Despite the fact that the deep sleep stage does not take long, it has a strong effect on the body. For example, young children with bedwetting may experience involuntary urination during this time In persons prone to sleepwalking, it is at this stage that attacks of this disease can occur.     

REM sleep stage

This phase was discovered not so long ago (in 1953) and is still being comprehensively studied. It was found that a state of quick rest follows immediately after a deep one and takes about 10-15 minutes in duration. 

REM sleep is the time when brain activity is expressed in the production of waves that are close in frequency to beta waves. Fluctuations in brain activity during this period are very intense and fast. Hence the name – “fast”. Also during this period in the scientific literature as phase REM or REM-sleep.      

A person in this stage is completely motionless. His muscle tone drops sharply, but his brain activity is close to the state of wakefulness. The eyeballs move under the closed eyelids. 

The connection between vivid, memorable dreams and this phase is most clear. While in it, a person sees the most colorful images and plots. If you initiate awakening during REM sleep, in 90% of cases, a person will be able to retell their visions.       

When asked how long this phase of sleep lasts , scientists cannot give a clear answer. Its duration is approximately equal to 20-25% of the total time of night rest. The phase of REM sleep , like NREM sleep, has a cyclical structure. By the nature of brain activity, the cycles are similar, but they differ in duration.     

The first cycle occurs approximately 1.5 hours after falling asleep. The time of the next one increases slightly and so on. In the morning, the duration of the last phase of REM sleep can reach several tens of minutes. In this case, a person sleeps shallowly until, finally, he wakes up completely.    

Closer to the morning, the activation of all systems is observed in the body. The hormonal system begins to work more actively. In men, there is an erection of the penis, in women – the clitoris. Respiration and heart rate change. The rises and falls of blood pressure alternately replace each other.

Waking up in different phases and rest cycles  

The general health and well-being of a person directly depends on the quality and duration of night rest, which has a heterogeneous structure. During the night, the human brain needs to go through the described stages. Only under this condition will the body fully recover.

Moreover, all phases are equally important. Slow, fast, deep sleep – they all perform important functions. Having learned what a person’s deep sleep is, scientists have established that it is necessary for normal mental activity and the maintenance of the skills acquired throughout the day. Fast regulates energy resources. Its absence can lead to the death of the body.    

The deepest sleep phase is the hardest to wake up. Neither body nor mind is ready for awakening. At this time, complex neurochemical processes take place in the brain, which it is better not to interrupt. Knowing what a person’s deep sleep is, it is easy to understand its significance for the safety of the nervous system.     

But during a lung it is quite easy to wake up. At this time, the body is ready to be awake and all brain stabilizing processes are complete. However, a chronic lack of REM sleep is very bad for your health, so doctors advise you to get enough sleep.  

How much sleep do you need

The optimal length of night rest for each person is highly individual. For some, 7 hours is enough for a full recovery, for others, 10 is not enough. And yet there are norms for each age group. With their help, it is easy to determine if a person is sleeping enough:

  1. Babies in the womb and newborns rest for 17 hours. And that’s okay. During rest, their brains and bodies grow and develop.
  2. In babies 3-11 months, sleep gradually decreases to 12-15 hours.
  3. Preschoolers sleep a little less (10-13 hours).
  4. Teenagers need 8-10 hours of night rest. Young people 17-18 years old – 7-9 hours.
  5. Adults should sleep approximately the same amount (7-9 hours).
  6. The rest of retirees is usually reduced by 1-2 hours, and this is also normal.

Falling time and value of sleep 

The quality of rest depends on when a person goes to sleep. Doctors advise going to bed early, and this is no accident. Going to bed at 20:00, a person provides himself with a full 7-hour rest and very deep sleep with high-quality restoration of all body functions.  

Anyone who goes to the bedroom after 22:00 “shines” about 4 hours of full sleep. The situation is very bad for citizens who are used to going to bed closer to dawn. If you fall asleep at 3:00, then at such a late time the deep sleep phase will last no more than 15 minutes.   

The value of the sleep of a person who spent the whole night on his feet and “nodded” only in the morning is equal to one minute. Naturally, in such a regime, neither physical nor intellectual capabilities will be restored. If you live in such a regime for a long time, you can notice problems with memory and concentration, constant fatigue and absent-mindedness.

In general, everyone needs to go through all the phases by hours from 21: 00-22: 00 until dawn. Only in this case the person will be healthy and full of energy. People who do not get enough sleep suffer not only from chronic fatigue, but also from a host of diseases. Among them are neuroses, hypertension, oncology, etc. In addition, chronic lack of sleep significantly reduces life expectancy.      

How deep sleep should be 

People who have lived for thousands of years without electricity and the Internet went to bed at sunset. It seems strange now. However, modern citizens do not take into account the fact that over millions of years of evolution, the human brain has adapted to navigate according to the movement of the daylight. It’s natural for him.

By changing this regime set by nature, he condemns himself to illness and premature old age. Now, knowing what deep human sleep is and what the value of a night’s rest at different times is, it is easy to understand the importance of each phase.  

It is important to adjust your individual regimen. Falling asleep early and a long night’s sleep is the path to beauty, health and longevity. It helps to burn excess fat and restore wasted energy, improves memory and suggests answers to questions that for some reason stubbornly do not want to be solved during the day.

Leave a Reply