Describes recognized sleep disorders and explains how doctors diagnose and treat them, and how people with sleep disorders can cope. Explores circadian disorders (mismatches of the body’s internal clock with the rest of the world), parasomnias (disorders of arousal or the interface between sleep and waking), dyssomnias (disorders of getting to sleep or staying asleep or of excessive sleepiness). Clarifies the many types of insomnia and how excessive daytime sleepiness lowers the quality of life for millions of people.