Chapter 4: Stress Management and Sleep 87 NREM is a deeper state of sleep, as compared to REM sleep, and is where most of physical restoration associated with sleep occurs. NREM can be further classified into three stages: stage I, stage II, and stage III. Stage I is a transitory phase of sleep lasting only about 10 minutes. During this phase, individuals are easily awakened. In fact, individuals who are awakened from stage I sleep often claim they were not yet asleep (Coren, 1996). Stage II is where actual sleep begins as serves as a transition period between light sleep and deep sleep. This stage of sleep usually lasts between 5-20 minutes. Individuals who are awakened during this phase would admit to being asleep. Stage III is the deepest stage of sleep and where the majority of physical restoration occurs. In fact, research has shown that chronic lack of stage III sleep can permanently stunt growth (Dement & Vaughan, 1999). During this phase, the blood supply to the brain is decreased and all but the essential bodily functions are shut down (Walters & Byl, 2021). Stage III sleep generally lasts from 10 minutes to one hour. REM sleep begins at the end of Stage III sleep (i.e., approximately one hour after falling asleep). REM sleep is similar to being awake in that it is a period of intense brain activity. In fact, REM sleep is when most dreams occur. During REM sleep, heart rate and blood pressure increases; breathing becomes more rapid, irregular, and shallow; the eyes rapidly move in various directions (thereby coining the term REM); and the skeletal muscles relax (Walter & Byl, 2021). One cycle of REM sleep lasts between 1-20 minutes. A complete sleep cycle (i.e., stage I, stage II, stage III, REM) lasts about 90 minutes and is repeated several times per night. In subsequent cycles, the amount of time spent in deep sleep gets shorter and the amount of time spent in REM sleep gets longer. A brief description of the various categories of sleep are provided in Table 4.2. Table 10.1 Stages of Sleep. NREM REM Stage I Stage II Stage III - Description Light Sleep Transitory Period Deep Sleep Dreams Occur Duration 10 minutes 5-20 minutes 10-60 minutes 1-20 minutes Sleep Deprivation Studies have shown that the majority of Americans are sleep deprived (Murphy & Delanty, 2007). Sleep deprivation is a condition where the amount of sleep received fails to meet the physiological needs of the body and mind. Although, occasional sleep deprivation is inevitable, chronic sleep deprivation is
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