Narcolepsy or Excessive Daytime Sleepiness – Narcolepsy is a chronic sleep disorder which causes excessive daytime sleepiness and drowsiness. Although not well understood it may be caused by genetic factors and abnormal signaling in the brain. Narcolepsy can cause sudden sleep attcks, loss of muscle tone, and hallucinations when falling asleep. Diagnosis is made through sleep tests and treatment may include stimulants, antidepressants, and other medications.