Chapter 17: Sleep and Sleep-Wake Disorders

The sleep-wake cycle represents a coordinated biological rhythm alternating between periods of wakefulness characterized by heightened mental activity and energy utilization, and sleep characterized by reduced consciousness and restorative physiological processes. Sleep architecture itself consists of distinct stages including non-rapid eye movement sleep, which progresses through light sleep into slow-wave sleep where the brain exhibits synchronized delta wave activity, and rapid eye movement sleep, characterized by vivid dreaming and paradoxical muscle atonia despite cortical activation. The chapter surveys a range of pathological conditions disrupting normal sleep patterns, including narcolepsy, an autoimmune neurological disorder marked by sudden loss of muscle tone and intrusive rapid eye movement sleep episodes during wakefulness, and restless legs syndrome, a movement disorder involving uncomfortable sensations in the lower extremities that interfere with sleep initiation and maintenance. Respiratory sleep disorders such as obstructive sleep apnea involve repeated collapse of the upper airway during sleep, causing oxygen desaturation and fragmented sleep architecture. Circadian rhythm disorders encompass disturbances in the timing of the sleep-wake cycle, including non-24-hour sleep-wake disorder affecting individuals with absent light perception and adjustment disorders following rapid time zone changes or rotating shift work schedules. Diagnostic assessment typically begins with detailed sleep diaries or actigraphy records maintained over at least two weeks to document sleep duration, nighttime awakenings, sleep quality ratings, and daytime functioning patterns. Treatment approaches vary by disorder type and may include behavioral interventions such as stimulus control and sleep restriction therapy for insomnia, pharmacological interventions including hypnotics or stimulants depending on the condition, continuous positive airway pressure therapy for obstructive sleep apnea, and circadian phase adjustment strategies for rhythm disorders.