The Stages of SleepSleep is divided into two distinct types: Non-REM (NREM) sleep and rapid eye movement, or REM sleep. When you first go to sleep, you begin NREM sleep, also known as “quiet sleep,” and then go through four distinct phases, each one progressively deeper than the other. In Stage I, your muscles begin to relax, your breathing becomes regular, and body temperature starts to drop. You can be awakened easily from this early and shallow stage of sleep. During Stages II and III, your sleep becomes deeper, with your body processes slowing down. It’s difficult to awaken you, and if you are suddenly awakened, you may be groggy or startled and not know where you are. Delta sleep, or Stage IV sleep, is thought to be the restorative stage when the body goes about its various repairfunctions. During REM sleep, the next major sleep phase, your mind is hyperactive but focused. At this time, your blood pressure soars and then sinks low. Your heart rate races and slows, and your breathing pattern is uneven. Blood flow to your brain increases. Dreams are common and often vivid. Erections are also common, as are engorgements of the clitoris. Except for a quick fluttering back and forth of your eyelids, there is no noticeable physical motion while you are in REM sleep because your body’s motor system has been shut down. A typical sleep cycle begins with NREM sleep and ends with REM sleep, with the two combined cycles lasting a total of 90 to 100 minutes. This sleep cycle is repeated four to five times during the night. Early at night, the REM period may only be five minutes long but it may stretch to an hour as the night progresses. However, if you are a poor sleeper—perhaps because of sleep apnea—you may spend less time in Stage IV and REM states, with your cycles fragmented and disrupted by periods of wakefulness. |
