National Sleep Foundation

Chapter 4: Primary Hypersomnias

Idiopathic Hypersomnia: Overview

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

Individuals who have idiopathic hypersomnia take frequent naps that are un-refreshing, have difficulty waking up, and experience post-awakening confusion (also known as “sleep drunkenness”). Compared to patients who are long sleepers, patients with idiopathic hypersomnia never feel fully refreshed and awake. Simply increasing the total time spent in bed does not resolve the EDS. An increased amount of time spent asleep is not a feature of idiopathic hypersomnia.68


  1. Bassetti C, and Y Dauvilliers, “Idiopathic Hypersomnia,” In: Kryger MH, Roth T III, Dement WC, eds. Principles and Practice of Sleep Medicine (5th edition), Philadelphia, Pa: Elsevier Saunders; 2011:969-979.