Narcolepsy is a chronic sleep disorder characterized by overwhelming daytime drowsiness and sudden attacks of sleep. People with narcolepsy often find it difficult to stay awake for long periods of time, regardless of the circumstances. Another common feature of narcolepsy is cataplexy, which is a sudden loss of muscle tone in response to strong emotion (such as laughing, surprise, or anger). These episodes of muscle weakness can cause an affected person to slump over or fall, which occasionally leads to injury. Episodes of cataplexy usually last just a few seconds, and they may occur from several times a day to a few times a year.
Many people with narcolepsy have a low level of hypocretin (also known as orexin). This is a chemical made in the brain that helps you stay awake. In some people with narcolepsy, there are fewer of the cells that make this chemical. This may be due to an autoimmune reaction.
Researchers have identified changes in several genes that influence the risk of developing narcolepsy. The most well-studied of these genes is HLA-DQB1, which provides instructions for making part of a protein that plays an important role in the immune system.
Related to:
Cataplexy, Daytime drowsiness, sleep attacks