Introduction

Sleep and rest are requirements for life. Both of them can refresh and restore. Although the terms are sometimes used synonymously, they do not reflect exactly the same concepts. Rest tends to be a more temporary construct, associated with a break from stress and exertion. Relaxation is commonly correlated to rest; indeed, the phrase “rest and relaxation,” or R & R, is a frequently used colloquialism. Although sleep incorporates rest, rest does not necessarily involve sleep. Sleep involves complicated neurophysiological processes that influence growth and development of the entire body, including the brain. The sleep state reduces consciousness and related neurological activity, with accompanying decline in body functions, including cardiopulmonary responses and metabolism. During nonsleeping rest, a person reduces metabolic demands, but remains alert, with muscle tone and potential for immediate responses intact.

Significant physiologic changes occur at different stages of the sleep cycle. Such changes include fluctuations of heart and respiratory rates, temperature, brain activity, and oxygen demands. Even muscular movement varies by sleep stages, notably during the rapid eye movement (REM) stage. Effects of sleep, and of sleep deprivation, can be apparent in resultant physiological changes, behaviors, and actions. Medical conditions, including kidney disease, cardiovascular problems, and a decline in immune function, are all possible repercussions of insufficient sleep. Inadequate sleep can also result in various psychological disorders and behavioral changes.