Chapter 4: Stress Management and Sleep 86 Sleep Regulation Sleep is regulated by two systems: sleep-wake homeostasis and internal circadian biological clock. Sleep-wake homeostasis creates a balance between sleep and wakefulness. After long periods of being awake the need for sleep accumulates and signals to the body that it is time to sleep. Sleep-wake homeostasis also helps to ensure enough sleep is accumulated at night to account for the hours of wakefulness. The internal circadian biological clock, also known as circadian rhythm, regulates feelings of sleepiness and wakefulness over a 24-hour period. The internal circadian biological clock fluctuates and causes you to feel more alert and sleepier at certain points throughout the day (Dement & Vaughan, 1999). The internal circadian biological clock prefers consistency. Significant disruptions to normal sleeping patterns, such as when traveling to different time zones, can result in excessive sleepiness, loss of concentration, poor motor control, increased irritability, slowed reflexes, and nausea (Smolensky & Lamberg, 2000). This condition is commonly referred to as jet lag. Interestingly, the circadian clock is not constant but changes throughout life. For example, the circadian clock is significantly different during adolescence than it is during childhood and adulthood. Research has shown that increases in melatonin (a hormone released at night to promote sleep) levels occur later at night for adolescents than it does for children and adults. This delayed release of melatonin can cause adolescents to feel more alert at night thus making it difficult for them to fall asleep before 11:00 p.m. (Walters & Byl, 2021). This problem is compounded when they must get up early for school and/or other commitments thereby making it difficult for them to the necessary amount of sleep (9.25 hours per night on average, 8.5 hours per night minimum). To help combat this, the National Sleep Foundation recommends dimming the lights as bedtime approaches to help boost melatonin levels thereby making it easier for adolescents to fall asleep earlier. Additionally, exposing them to bright lights as soon as possible in the morning may help them wake up and feel more alert sooner (National Sleep Foundation, n.d.; National Sleep Foundation, 2010). Sleep Architecture Sleep phases can be classified into two primary categories: nonrapid eye movement (NREM) and rapid eye movement (REM). In normal adults, NREM accounts for approximately 75 percent of sleep and REM accounts for approximately 25 percent of sleep (National Sleep Foundation, 2006).