What is Sleep?
Sleep is a mental and physical state of rest, during which time the person is usually inactive. Sleep is usually accompanied by a decrease in body temperature, blood pressure, respiration rate, and most bodily functions. However, one’s brain remains active during sleep. In fact, tasks such as storing of short-term memory material into long-term memory and replenishment of neurochemicals occur during sleep.
Structure of Normal Sleep
There are two distinct types of sleep:
1. Rapid Eye Movement (REM) sleep (also known as dreaming sleep)
2. Non-REM (NREM) sleep.
Sleep is composed of 5 stages.
Stages I-IV are known as NREM sleep (with stages III & IV being deep sleep.
Stage V is REM sleep.
Humans generally alternate between REM and NREM in 90-110 minute cycles. Once asleep, we move into stage I, and then we cycle through stages II – IV in roughly 30 -40 minutes. We cycle back briefly through stage III & II, then to stage 5 (REM). This process normally occurs 4-5 times per night.
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