Idiopathic hypersomnia is a sleep disorder that presents as excessive daytime sleepiness. It is a primary sleep, neurologic cause of long-sleeping, sharing many similarities with narcolepsy. People with idiopathic hypersomnia may sleep for 10 hours or more and still not feel refreshed. Upon testing these patients with sleep studies, including a multiple sleep latency test called MSLT, they do not fully meet the criteria for narcolepsy with 2 sleep onset REM periods but may meet the hypersomnia criteria of a mean sleep latency of less than 10 minutes. It is a diagnosis of exclusion as narcolepsy has to be ruled out.