The MDH phase (slow eye movements) takes about 75% of the sleep time – and is divided into four stages.
♦ Stage 1: transition between sleep and wakefulness, when you almost fall asleep, but … not really. Have you ever had to wake up and turn on the light because of a suspicious shade, sit in bed, being sure that you heard someone call you by name? Or, maybe, before you start and wake up, did you experience the sensation of a fall? All this happens at the first stage of the most shallow sleep – when dreams seem to be mixed with reality. Muscle movement slows down, there may be cramps, an unpleasant sensation from which can also wake you up.
♦ Stage 2: immersion with sleep. You disengage from the environment and listen less to the outside world. The body temperature drops, the respiratory and heart rhythms slow down. This is still considered a relatively shallow sleep, although adults spend almost half of the time sleeping that way.
♦ 3rd and 4th stages: the last stages of MDH sleep are usually combined, since the 3rd is a transitional stage to the 4th. This is the deepest and most restorative sleep, called “delta sleep”, or “synchronized sleep.” The fourth stage is proudly called the “absolute delta”: it is thanks to her that your body begins to recover and rest. The blood pressure decreases, the respiratory and heart rhythms become maximally slow, uniform, the blood rushes to the now completely relaxed muscles, promoting tissue growth and their recovery. Growth hormones flood the body (in children and adolescents), and the brain begins to reinforce what you learned during the day, organizing information like a business secretary. When you wake up at this stage, you feel shocked, weak, and for a few minutes you lose orientation.
BDG sleep is the fifth stage and the last part of the cycle preceding its repetition. It accounts for 25% of total sleep time.
♦ Stage 5: owes its name to the rapid movement of the sleeper’s eyes (the eyes are usually closed, but not always). It was discovered in 1953 by American neurophysiologists Nathaniel Kleitman and Eugene Acerinski. The speed of one rapid movement of the eye is called the density of BDG. At this stage, brain waves are similar in their characteristics to waves at rest.
This type of sleep is characterized by electrical activation of the brain, which causes rapid, rapid eye movements under closed eyelids. Although you can see dreams in all five stages, they are more likely to occur at this very moment; they believe that the eyes move because you follow the pictures of your dream – watch a movie that scrolls in your head.
In fact, the eyes do not send any visual information to the brain, but, as studies have shown, the visual cortex is activated. She does something, although it is not entirely clear what. Scientists think that this may be part of the process of memory formation or fixation — when the brain orders everything that has happened in a day. Perhaps this is so, but brain signals paralyze the muscles, so you are not able to go beyond your sleep and act.
This is a relatively shallow stage of sleep, when the respiratory rhythm rises and the blood pressure rises, and the brain polishes to the brilliance of the memory and blows dust particles off the accumulations, bringing you to a state of readiness for the coming day. An ordinary person experiences from three to five episodes of BDG overnight, and the first episode begins, as a rule, 70–90 minutes after falling asleep.
In order to wake up fresh (s) and, if possible, not to resemble a zombie, each stage of sleep during one night should last for a certain time. As a rule, it is distributed as follows:
♦ 1st stage: 5% night time ♦ 2nd stage: 50%
♦ 3rd and 4th stages: 20%
♦ 5th stage: 25%