The Cleveland Clinic

Sleep Disorders: Sleep 101

Introduction to sleep

When you sleep, your body rests and restores its energy levels. However, sleep is an active state that affects both your physical and mental well-being. A good night's sleep is often the best way to help you cope with stress, solve problems, or recover from illness.

What Happens During Sleep?

Sleep is prompted by natural cycles of activity in the brain and consists of two basic states: Rapid Eye Movement (REM) sleep and Non-REM (NREM) sleep, which consists of Stages 1 through 4.

During sleep, the body cycles between non-REM and REM sleep. Typically, people begin the sleep cycle with a period of non-REM sleep followed by a very short period of REM sleep. Dreams can occur in any stage of sleep.

What Is Non-REM Sleep?


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