Table 1.

Intrinsic and extrinsic causes of excessive sleepiness and impaired alertness

INTRINSIC	EXTRINSIC
Narcolepsy Sleep-related breathing disorders Circadian rhythm disorders Idiopathic hypersomnia Restless legs syndrome/periodic limb movement disorder Medical conditions Psychiatric disorders Mood disorders (e.g., major depressive disorder, atypical depression, seasonal affective disorder) Psychosis (e.g., schizophrenia) Medication-induced disorders	Sleep deprivation Poor sleep hygiene Chronic alcohol or drug use Sleep disruption related to consumption of coffee, cola, and other caffeinated beverages