This document discusses various types of sleep disorders including insomnia, parasomnias like night terrors and sleepwalking, and circadian rhythm disorders. It describes the normal sleep cycle and stages including REM sleep and the different non-REM stages. It notes that REM sleep occurs in cycles throughout the night, increasing in duration closer to morning, while deeper non-REM sleep stages are more prominent in the first half of the night. Several specific sleep disorders are also outlined such as narcolepsy, sleep paralysis, and delayed or advanced sleep phase disorder.