Narcolepsy is a rare sleep disorder characterised by sleepiness to the point of involuntary napping. All people with narcolepsy have extreme levels of fatigue and sleepiness during the day, but how this manifests itself can differ. For instance, some people with narcolepsy might fall asleep for 10 to 20 minutes several times every day, whether they want to or not. Others with this condition have more control over their naps, and can choose when and where they will sleep, (for example, during lunch breaks). Narcolepsy can develop at any age, but it commonly starts either during the teenage years or in middle age. A person with narcolepsy usually has the condition for life.

A malfunctioning brain structure called the hypothalamus is at fault. Mild cases of narcolepsy can be managed with regular naps, while severe cases need medication.