Sleep disorders are defined as disorders in falling asleep, sleep retention and sleep duration or abnormal sleep behaviors such as night terrors or sleepwalking. According to statistics, 45% of people in China have varying degrees of sleep disorders. Sleep is essential for survival and good health, but the causes and mechanisms are not fully understood. Individual sleep requirements vary widely, with healthy adults requiring as little as 4 hours of sleep per day and as long as 9 hours. Most people sleep during the night. Some people sleep during the day to accommodate their work, but this often causes sleep disturbances. There are many factors that affect an individual’s sleep, including agitation and emotional depression. Medications also have an effect on sleep: some make people fall asleep, while others cause difficulty sleeping. Some foods and food additives, such as caffeine, overly hempy foods and monosodium glutamate (MSG), can also affect sleep. Sleep is not a homogeneous process; it can be divided into several time phases that cycle 5 to 6 times per night, respectively. Sleep can progress from stage 1 (the lightest stage of sleep, the easiest to wake up) to stage 4 (the deepest stage of sleep, the hardest to wake up). In stage 4, muscles are the most relaxed, blood pressure is at its lowest point, and heartbeat and breathing are the slowest. In addition to the above 4 stages, there is another type of sleep with rapid eye movement (REM) and behavioral activity. During REM, the EEG activity is high and nearly waking. The changes in brain waves that accompany REM sleep can be recorded by electroencephalography (EEG). in REM sleep, the rate and depth of breathing increases, and the muscles are at their most relaxed to the point of being lower than in the deepest stages of non-REM sleep. Most dreams occur in REM and stage 3 sleep, while most sleep talk, nightmares and sleepwalking occur in stages 3 and 4. In normal nocturnal sleep, REM sleep can occur immediately after non-REM stage 4 in any of the 5-6 cycles, but can also occur in either stage. Timing of sleep cycles:Normally sleep cycles 5 to 6 cycles per night. The deep sleep phase (stages 3 and 4) is relatively short. Most of the time is spent in the rapid eye movement (REM) sleep phase, but this phase is often interrupted by the light sleep phase (phase 1). There are brief awakenings throughout the night. If you develop a sleep disorder, you should actively seek medical attention to identify the cause early and give aggressive treatment. Long-term sleep disorders can be secondary to many diseases.