Characteristics and Determinants of Normal Sleep

Although sleep appears to simply be a body and mind at rest, it is actually a dynamic and complexphysiologic state that is necessary for survival. Normal sleep is characterized by behavioral and physiologicchanges as well as 2 distinct sleep states, rapid eye movement (REM) and non-REM (NREM).Throughout the course of a night, people cycle between NREM and REM sleep via an ultradianrhythm, with most of sleep spent in NREM. Determinants involved in the regulation of sleep are thehomeostatic and circadian processes. Despite being highly regulated, sleep is fragile, and its stagesand duration may be affected by multiple factors, such as age, drugs, temperature, and medical andpsychiatric disease. Variations in nighttime sleep impact subsequent sleep periods as well as daytimefunction.