Sleep Phases and What is Important To Know About Them

Cycles, stages and rhythms of night rest

The phrase “sleep phase” sounds beautiful and mysterious, intriguing with the cognitive implication hidden behind a capacious concept. You have probably heard that sleep is fast or slow, but you also probably do not remember all the subtleties of the above definitions. And since the quality of night rest becomes more and more valuable every year, it will not be superfluous to re-master the physiology of sleep phases and figure out what is the difference between REM and slow sleep.


The scientific diagram of the structure of human sleep includes two main phases: slow-wave sleep (aka slow-wave, orthodox, or Non-REM sleep) and rapid sleep (REM or REM sleep – an abbreviation for rapid eye movement).

Sleep of a healthy person with a normal schedule in accordance with biological rhythms is a cycle of two basic phases (each of which, in turn, has certain stages), repeating several times during the night. Sleep phases of a person have different durations and special functional tasks due to the activity of brain structures.


Falling asleep, a person plunges into the phase of slow sleep, or rather, into its first stage, which lasts 5-10 minutes. In fact, this is a “prelude” to rest, the transition of the body from an active state to complete relaxation: the frequency of respiration and pulse decreases, metabolism slows down, eye movement under the eyelids, temperature drops, brain waves slow down, muscles relax (sometimes with impulsive twitching).

Then comes the second stage, which lasts about 20 minutes – shallow or light sleep, during which muscle activity, temperature, heart rate continue to decrease, and the eyes stop moving. The stage of light sleep, repeating, like others, several times, takes about 45-55% of the total time of night rest.

Another 30-45 minutes falls on the third and fourth stages – deep delta sleep sets in. Heartbeat and breathing move to the slowest rhythm, brain waves and muscles are completely relaxed. It is during this period that a person is very difficult to wake up, he / she is fast asleep and even if he talks in oblivion, then he does not remember anything.

After that, the sleeping person returns to the 2nd stage of slow wave sleep, which is replaced by the first short session of REM sleep lasting about 5 minutes. The described sequence of stages is called a cycle, the first of which lasts 90-100 minutes, and, on average, healthy sleep lasts 4-5 full cycles, depending on the age and needs of the body. Speaking about the norms for a particular phase of sleep, it is worth noting that when the cycles are repeated, the proportion of slow sleep decreases, and fast sleep increases.


During slow wave sleep, and especially in the third and fourth stages, the body restores energy and physiological resources, starting the processes of cell regeneration, improving the blood supply to muscles, and generally strengthening the immune system. While we sleep soundly, the pituitary gland works to release substances that are important to the body, such as growth hormone, which promotes the development and repair of muscle and bone tissue.

In addition, deep sleep helps to structure the unrestrained flow of information flowing into it, allowing the brain to form lucid memories, supporting short / long term memory and general learning.


The phase of REM sleep or paradoxical sleep is characterized by increased activity of the brain, which is manifested in the rapid movement of the eyeballs, noticed by the researchers. The activity of the brain, like the pulse rate, in these minutes approaches the state of wakefulness, breathing becomes more frequent.

During the phase of REM sleep, the brain filters the information received during the day, discarding unnecessary and secondary ones. Somnologists believe that those who wake up at the REM phase are more creative and ready to tackle extraordinary problems. We also see dreams – 80% of dreams occur during REM sleep, and those who wake up during this period usually remember what they dreamed and describe in detail what they saw.

How to get enough sleep, taking into account your sleep phases?

A good night’s sleep is just as important as proper nutrition and regular workouts. Lack of sleep, according to scientists, causes a wide variety of health problems – from excess weight, prediabetes and depression to reduced immunity and sexual desire.

The most effective method to guarantee a sound and healthy sleep is to follow the regimen. Taking into account personal needs and knowing how many cyclic repetitions of sleep phases the body needs to get a good rest, determine the hour when it is better for you to wake up and when it is better to fall asleep, and follow this schedule, going to bed and leaving it at the same time – every day clearly and under any conditions.

Here are some more tips to help you get enough sleep without disturbing your circadian rhythm and by following how your sleep phases follow each other clockwise:

  • exercise – at least 20-30 minutes a day, avoiding training a few hours before bed;
  • in the afternoon, drink only decaffeinated water and drinks – coffee, alcohol and nicotine make it difficult to have a good night’s rest;
  • tune in to rest after a long day – read a book or take a bath;
  • get rid of bright lights and loud noises in the bedroom – TV, laptop and, preferably, a smartphone;
  • if you can’t sleep, do not lie in bed, tossing and turning, but rather get up and do something calm, for example, read, until you start to feel sleepy again;
  • consider replacing pillows, blankets, buying soft and breathable bedding, or rearranging your bed – perhaps you need a more comfortable nest to sleep like a child.