National Sleep Foundation

Chapter 4: Primary Hypersomnias


Hypersomnia is a serious and debilitating disorder with no known cause1.  Its primary complaint is excessive daytime sleepiness (EDS) — having trouble staying awake during the day — that does not improve when the person gets more sleep. Further, the EDS is not caused by "disturbed nocturnal sleep or misaligned circadian rhythms."2  Other sleep disorders may occur at the same time, such as sleep-disordered breathing syndromes. They must be diagnosed and treated before the hypersomnia can be adequately assessed.

Primary hypersomnias include narcolepsy, idiopathic hypersomnia, and Kleine-Levin syndrome, each of which is described in this chapter. This chapter also discusses behaviorally-induced insufficient sleep syndrome (ISS), which is the most prevalent cause of EDS.

(Secondary hypersomnia, in which EDS is a symptom or cause of another disorder, is very common, and is not discussed in this chapter. It can be caused by a range of physical and mental health conditions, occur as a side effect of medications, or result from substance abuse.)

It is estimated that approximately five percent of the general population is affected by hypersomnia; men have higher rates, due to sleep apnea syndromes.3


  1. National Sleep Foundation, Sleep Disorders: Extreme Sleepiness, Arlington, VA: NSF, no date. Available online at
  2. Thorpy M, “Classification of Sleep Disorders,” In Kryger M, Roth T, Dement W (ed.), Principles and Practice of Sleep Medicine (5th Edition), St. Louis: Elsevier Saunders, 2011, page 684.
  3. Dauvilliers Y, “Differential Diagnosis in Hypersomnia,” Current Neurology and Neuroscience Reports 2006; 6(2): 156–162. doi:10.1007/s11910-996-0039-2.