Abstract
Excessive daytime sleepiness (EDS) is one of the leading reasons that patients present to sleep clinics. Approximately 10% to 14% of the adults report that excessive sleepiness interferes with their daily lives. Common causes of EDS include obstructive sleep apnea, sleep deprivation, circadian rhythm disorders, medication effects, psychiatric conditions especially depression, and primary hypersomnia such as narcolepsy or central idiopathic hypersomnia. Vitamin B-12 deficiency is a rare cause of EDS. We are presenting a case of severe vitamin B-12 deficiency as an unusual and rare cause of hypersomnia.