Sleep can be divided into five stages, in these five stages, brainwaves have different behaviors, the frequency of brainwaves into the sleep stage will decline.
In the first and second phases, the human body sleeps more lightly, but the body gradually relaxes, breathing and heart rate getting slower. In the third and fourth phases, the human body goes into deep sleep, blood pressure, respiration, and heart rate reach the lowest point of the day, the blood vessels begin to swell, and the blood stored in the organs during the day begins to flow to muscle tissue, nourish and Fix them. If you wake up in a deep sleep, you will find it hard to get up, slow reaction, lack of sense of direction, go to the bathroom in the middle of the night and even do not remember it. The fifth phase is the Rapid Eye Movement (REM), when people are dreaming mostly at this stage.
After categorizing the different stages of sleep, the first important concept - Sleep Cycles. The sleep cycle refers to the different stages of the body going to sleep many times during sleep. Among them, the first deep sleep time is the longest of all deep sleep, and then continue to shorten, or that the body most of the first three or four hours sleeping in deep sleep; the first REM in the REM is the shortest, then grows longer.
High-quality sleep is easier for the brain to enter the deep sleep stage, and stay deep enough in the deep sleep stage. So, how to get high-quality sleep, we must control the body's sleep clock (The Inner Sleep Clock). The so-called sleep biological clock is a potential system in the body telling the body when it feels tired and when it awakens, controlling the depth and timing of sleep in the body.