Cause		Comments
Primary hypersomnias of central origin
Narcolepsy		0.02 to 0.18 percent of population
Idiopathic hypersomnia		10 percent of patients with suspected narcolepsy
Other rare primary hypersomnias		Example: Kleine-Levin syndrome
Secondary hypersomnias
Sleep disorders
	Sleep-related breathing disorders	Excessive daytime sleepiness secondary to obstructive sleep apnea (general population prevalence is 2 percent of women and 4 percent of men)
	Behavioral sleep deprivation	Especially common in adolescents and shift workers
	Other sleep disorders	Includes circadian rhythm sleep disorders, sleep-related movement disorders
Medical or psychiatric conditions
	Medication effects	Includes prescription, nonprescription, and drugs of abuse
	Psychiatric conditions	Especially depression
	Medical conditions	Includes head trauma, stroke, cancer, inflammatory conditions, encephalitis, neurodegenerative conditions