The Mystery of Sleep~ Rest for the body, Activity for the brain ~Everyone sleeps. While humans sleep, they do not procreate, protect or raise their young, gather food, earn money, write papers, etc. Surely, at least once, most people have wondered why they sleep despite these disadvantages. According to Greier (48), it is difficult for scientists to answer the seemingly simple question of what exactly sleep is for. Sleep takes up a third of human life, which seems like a waste of precious time; however, no one can survive without sleep. According to Shelton (5), drowsy drivers cause approximately 56,000 traffic accidents in the United States each year. Furthermore, Wolfson and Carskadon (875) interestingly report that students who achieve good grades sleep longer than students who struggle or fail in school. Furthermore, the Chernobyl nuclear accident, the Three Mile Island near-meltdown, the environmentally disastrous Exxon Valdez oil spill, and the loss of the Space Shuttle Challenger were all caused by people making mistakes due to lack of sleep (Coren 1 ). Sleep deprivation appears to cause harmful effects on the daily lives of humans. Sleep is a state characterized by reduced consciousness, reduced skeletal muscle activity, and depressed metabolism. Humans normally experience sleep in patterns that follow five observable progressive stages (stages 0~4) of non-rapid eye movement (NREM) sleep and a separate pattern of rapid eye movement (REM) sleep (Coren 31). To measure the electrical activity of neurons during the stages: Stage 0 is not actual sleep, but going to bed and preparing for sleep. During Phase 1, ... half of the paper ...... (1997): 48-50.Hobson, Allan J. {Sleep}. New York: American Science Library, 1995.Meddis, Ray. {The sleep instinct}. Boston: Routledge & Kegan Paul, 1977. Moreno, Anne. "Why do we sleep? Getting a good night's sleep is important for your health and also for your success in life." {Current Health 2} 25.2 (1998): 6-13.Rechtschaffen, Allan. "Current Perspectives on Sleep Function." {Perspectives in Biology and Medicine} 41.3 (1998): 359-90.Shelton, Deborah L. "Sleep-deprived drivers linked to highway 'carnage'" {American Medical News} 38.26 (1995): 5-6.Stampi , Claudio , ed. {Why we nap: evolution, chronobiology and functions of polyphasic and ultra-short sleep}. By Jurgan Arnoff. Boston: Birkhauser, 1992. Wolfson, Amy R., and Mary A. Carskadon. “Sleep schedules and daytime functioning in adolescents.” {Child development} 69.4 (1998): 875-89.