It was only with the advent of modern technology that a thorough study and understanding of sleep mechanisms became possible. Although this topic had long interested researchers, it was technological advances that revealed that the body's purpose for sleep is not restful, as previously assumed.
Today, sleep is considered a special mechanism of self-regulation of the body's functions , and not just rest.
The sleep process is not uniform, so scientists studying human physiology have divided it into two phases:
1. Slow sleep , during which tissues damaged during the day and energy losses are restored, as well as energy reserves are accumulated for future activity.
It has been observed that the duration of this sleep phase depends on the intensity of physical activity during the day. The more energy and strength expended during the day, the longer the slow-wave sleep will last. This is likely the reason for the increased sleep duration seen in sick and recovering people, as well as the popular saying: “Sleep is the best medicine.”
2. Rapid eye movement (REM) sleep . During this phase, brain activity is similar to that of wakefulness.
There are observations that this phase is prolonged in people who have experienced stress or tension during the day. Based on this, it can be assumed that during REM sleep, the information received during the day is systematized. Figuratively, this can be compared to sorting a large amount of information from different fields by meaning, topic, and significance. The saying “The morning is wiser than the evening” applies precisely to REM sleep. Many have noticed that after a full night's sleep, they find the answer to a question they were actively pondering the night before.
It has now been established that after falling asleep , the following processes occur in the body:
- The loss of consciousness characteristic of the first stage of slow-wave sleep.
- Stage two of slow-wave sleep is typically characterized by decreased muscle activity, body temperature, and metabolic rate. Heart rate slows. Perception does not completely shut down at this stage. A person remains sensitive to some external stimuli.
- The third stage is characterized by the transition to full, deep sleep. This is the only period when brain activity decreases somewhat.
- During stage four, a person sleeps most deeply and typically does not remember the dreams they experience at this point. Sleep talking and sleepwalking are characteristic of this stage.
- A marked increase in brain activity is characteristic of REM sleep. Its functioning now resembles that of wakefulness. Muscles remain relaxed during REM sleep, with the exception of the oculomotor muscles, which experience rapid eye movement. This state of various bodily functions during REM sleep can lead to the development of sleep paralysis upon awakening during this period. This phase is also characterized by an increased heart rate and breathing rate, as well as an increase in body temperature. It is during this phase that the most vivid, emotionally charged dreams are experienced, which a person remembers and can recount upon awakening.
Restoring vitality after a hard day's work requires more than just physical rest. It requires a special state—sleep. It is during this period that the energy lost during the day is restored. The full sleep cycle must be repeated at least 4-5 times per night. Moreover, with each subsequent cycle, REM sleep occupies an increasing proportion of its structure.