How does deep sleep affect a person’s well-being and how long this stage should last


What is deep sleep

At night rest accounts for about a third of a person’s life, 7-8 hours a day. This physiological process helps to restore the body and goes through 4 or 5 consecutive cycles of changing the fast and slow phases.

The first (paradoxical) takes up to 15 minutes of time. The second – orthodox or slow sleep – lasts about one and a half hours, comes immediately after falling asleep, has 4 stages. The latter has the greatest effect on the body, the fourth – deep or delta sleep.

Significance of deep sleep

Why is the delta phase important in the process of night rest? During the day, the brain receives and processes a huge amount of various information, and its memorization is carried out in the delta phase. That is, the effectiveness of training and the level of intellectual development directly depend on the quality and duration of deep sleep. In addition to transferring the knowledge gained from short-term memory to long-term, physiological processes are of great importance.

In the course of scientific research it was found that the maximum of the muscles is noted in the deep stage. At the same time, catabolism slows down and anabolism is activated – the restoration of body cells. Toxins and other harmful waste products are derived from it, immunity increases.

Thus, a person fully rests exactly in the period of delta sleep. Changing its duration or failure of the entire cycle leads to chronic fatigue, drowsiness, weakening of the immune system, reduced intellectual ability.


Slow and fast sleep alternate all night cyclically. Falling asleep begins with the first, orthodox phase. It lasts about one and a half hours and passes in four successive stages:

  • Reduced alpha rhythm on EEG, the emergence of low-amplitude theta rhythms. At this time, the person is in a state of half-sleep, which may be accompanied by the appearance of dreamlike hallucinations. Thought processes continue, manifesting in the form of dreams and reflections on the events of the day. Often there is a solution to pressing problems.
  • The electroencephalogram registers the prevalence of theta waves, as well as the occurrence of characteristic rhythm increases – “sleepy spindles”. At this, the longest, stage, consciousness is turned off, the perception threshold rises, but it is still possible to wake the sleeper.
  • The appearance of high-amplitude delta waves on the EEG. In the third phase of slow sleep (from 5 to 8% of the total duration) they take less than half the time. As the delta rhythm prevails, the deepest delta sleep occurs.
  • In the fourth phase, which accounts for up to 15% of the night’s rest, the consciousness is completely disabled, it becomes difficult to wake the sleeper. During this period, most of the dreams occur, while the likelihood of manifestation of disorders (somnambulism, enuresis, nightmares) increases.

Orthodox sleep is replaced by a fast, the ratio is approximately 80% and 20%, respectively. In the paradoxical phase, the characteristic mobility of the eyeballs is observed; if the sleeper is awakened, he will recall the vivid dream of the sleep phase. The EEG shows electrical activity close to the waking state. Morning awakening occurs after 4 or 5 complete cycles in the “fast” stage.

Normal duration

What is the rate of deep sleep? Its duration and quality are determined by the individual characteristics of the human body. One is enough 4-hour rest, another to sleep, you will need at least 10. The duration is also affected by the age of the sleeper: in childhood it is up to 9-10 hours, in youth and maturity – about 8, and by old age it is reduced to a quarter of a day. The average ideal nighttime rest time is 7 or 8 hours, and the adult’s deep sleep rate is determined by the percentage ratio of the phases.

If we take the 8-hour sleep as a basis, the duration of a deep period in a healthy person will average 20%. That is, in general, it will take at least 90 minutes, and each of 4-5 cycles will take 20-25 minutes. With the reduction or increase of night rest time of each phase decreases or increases, respectively. However, their ratio in percentage terms does not change, and the body is fully restored.

Body processes

The electrical activity of the brain is described in the relevant section on the structure of sleep. How physiologically manifest all phases? At the beginning of falling asleep, the muscles relax, the pressure and temperature of the body decrease, breathing slows down. In the second period, these indicators increase, but it is still possible to wake a person, despite the partial disabling of consciousness and an increase in the perception threshold of external stimuli.

The deep phase, combining the 3rd and 4th stages, is normally characterized by complete muscle relaxation and a slowdown of all metabolic processes. It is difficult to wake up, and physical activity indicates the presence of disorders.

Causes of violations

Sometimes life circumstances require a reduction in deep sleep time (exam session or time trouble at work). A short-term increase in physical exertion or mental activity is quickly compensated. But if the duration of this phase decreases over time, chronic fatigue appears, memory deteriorates, and somatic diseases develop.

The reasons may be:

  • psycho-emotional overload, ;
  • diseases of the internal organs, nervous or endocrine systems;
  • forced waking at night (with prostatitis for emptying the bladder);
  • arterial hypertension.

All of these conditions require treatment and medical treatment, since delta sleep is vital to humans.

How to normalize deep sleep

The deep sleep phase should be at least 20% percent of its total amount. If chronic feelings of lack of sleep, fatigue and fatigue appear, it is time to think about how to increase the time for an adult to sleep slowly. Some measures can be taken independently: it is important to comply with the regime, going to bed no later than 22 hours and waking up no earlier than 6:00. Physical activity during the day and a relaxed atmosphere in the evening, combined with a light dinner, also contribute to the normalization of sleep.

Psychotherapy gives good results if the disorder has a psychogenic character. In some cases, medication is indicated, since it is not always possible to increase the duration of the deep sleep phase with physiological and psychotherapeutic methods. For this purpose, sedative and hypnotic drugs, calcium, magnesium and multivitamin complexes are used. Electrosleep is also prescribed – impact on the brain with low-frequency electrical impulses.


Delta-sleep plays an important role in the recovery and rest of the body, affecting the performance, well-being and quality of life. Any deviation from the norm in the form of lack of sleep, memory impairment and chronic fatigue should be treated without fail.

How does deep sleep affect a person’s well-being and how long this stage should last

Effective prevention is the observance of the regime and sleep hygiene, a healthy lifestyle, possession of relaxation techniques.

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