National Sleep Foundation

Glossary

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Idiopathic hypersomnia - A hypersomnia defined by the presence or absence of long sleep time (i.e., more than 10 hours). Idiopathic hypersomnia is diagnosed when patients have constantly severe excessive daytime sleepiness (EDS) for at least three months without other defining features, such as REM sleep abnormalities or cataplexy.

Insomnia - The most common sleep complaint, involves trouble getting to sleep and/or staying asleep, and/or experiencing sleep that is not refreshing.

Irregular Sleep-Wake Disorder - A Circadian Rhythm Disorder characterized by a lack of well-defined sleep-wake cycle; individuals with IST typically have three or more sleep episodes during a 24-hour period, rather than one major sleep period.