SLEEP CYCLES: AN RECURRING PHENOMENON
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The sleep cycle is an important part of how our sleep occurs. The sleep cycle refers to how our sleep patterns show a cyclic pattern, repeating the same stages over and over again during the extended periods that we sleep. Usually, the sleep cycle lasts 90 minutes before it repeats. As the night wears on, deep NREM-3 sleep grows short and disappears. The REM and NREM-2 sleep periods get longer. About 20 to 25% of sleep is spent in REM sleep. The diagram below is a hypnogram, which depicts the typical sleep cycle and the stages of sleep.