==Circadian rhythm== {{TNT|Further|Dark period}} The circadian rhythm is the body clock aligned to local solar time by light exposure and food intake, among other factors. It generates hormonal changes throughout the day consistently to produce effects on the body. One of the main effects is the secretion of [[Wikipedia:Melatonin|melatonin]], the presence of which is essential for entering SWS, and also affects the timing of REM sleep.
昼夜节律（Circadian rhythm）是体内的生物时钟，主要通过曝光和食物摄入等因素与当地的太阳时保持一致。它在一天中持续带动荷尔蒙变化，对身体产生影响。昼夜节律其中一个主要影响是褪黑素（melatonin）的分泌。它的存在对进入SWS至关重要，同时对REM的出现时间也会产生影响。
