Most people who have narcolepsy have low levels of hypocretin. This is a chemical in the brain that helps promote wakefulness. What causes low hypocretin levels isn't well understood.

Researchers think that certain factors may work together to cause a lack of hypocretin. These factors may include:

  • Heredity. Some people may inherit a gene that affects hypocretin. Up to 10 percent of people who have narcolepsy report having a relative who has the same symptoms.
  • Infections.
  • Brain injuries caused by conditions such as brain tumors, strokes, or trauma (for example, car accidents or military-related wounds).
  • Autoimmune disorders. With these disorders, the body's immune system mistakenly attacks the body's cells and tissues. An example of an autoimmune disorder is rheumatoid arthritis.
  • Low levels of histamine, a substance in the blood that promotes wakefulness.

Some research suggests that environmental toxins may play a role in triggering narcolepsy. Toxins may include heavy metals, pesticides and weed killers, and secondhand smoke.

Heredity alone doesn't cause narcolepsy. You also must have at least one other factor, such as one of those listed above, to develop narcolepsy.