Normal human sleep is divided into REM sleep and non-REM sleep, and non-REM sleep is divided into four periods, which are, in order, sleep onset, light sleep, moderate sleep, and deep sleep, making these four periods in order as one, two, three, and four. During REM sleep, brain activity and body metabolism react similarly to waking hours. During non-REM sleep, the metabolism of the whole body slows down, breathing, heart rate and blood pressure are reduced, the brain and the whole body are in a state of rest, the human cerebral cortex cells are in a full state of rest, which is extremely important for stabilizing emotions, balancing the mind and restoring energy, and at the same time, the human body can produce many antibodies to enhance the ability to resist diseases. During each night of sleep, the REM sleep period and non-REM sleep period alternate, alternating every night, in 4-6 cycles.