Regularly getting a good night’s sleep is crucial to both physical and mental health. During the sleep state, the body restores itself and memories are processed, benefiting our overall energy, alertness, and clarity of mind. How much sleep we need depends on our age and lifestyle, though it is generally agreed that adults should get approximately eight hours of sleep per night .
When our bodies sleep is defined in part by circadian rhythms, natural chemical processes that control our internal body clock. These patterns are normally tied to cycles of light, inducing sleepiness at night and waking us in the morning when it is light again. Melatonin, for example, is a hormone that induces sleepiness, lowers body temperature, and prepares the body for rest. Levels of melatonin naturally increase during the early evening as it begins to get dark, reach their peak in the middle of the night, and taper as morning arrives.
Despite the restful exterior of the sleep state, sleep is a dynamic, structured state of consciousness that progresses through several different stages with differing functions. The stages are defined by patterns of brain waves, muscle activity, and eye movements. During the early stages of light sleep, the muscles relax and the sleeper begins to drift from awareness of the conscious environment. The sleep gradually deepens, eliminating conscious awareness of the external environment until slow-wave sleep (SWS) is reached. The next phase is characterized by further changes to the brain waves, as well as rapid eye moments, and is thus dubbed rapid eye movement (REM) sleep. REM is also the stage of sleep where dreaming occurs. Following a period of REM sleep, the brain returns to SWS, continuing to cycle through the sleep phases throughout the night.
Sleep studies have shown that each of these phases is important for a satisfying night’s sleep. Disorders that prevent or interrupt the stages of sleep can cause a significant amount of physical and emotional distress, as a person never receives proper rest and rejuvenation.
