Its most common manifestation is an irresistible tendency to fall asleep, even in unlikely circumstances such as in the middle of a conversation or at a meal. These sleep attacks are brief periods of sleep during the person's normal waking. In order for narcolepsy to be diagnosed, a person must have suffered from the sleep attacks for at least three months. The other conspicuous symptom is a sudden loss of muscular control triggered by amusement, anger or excitement which is called cataplexy.
Some disorders have similar or even the same symptoms.
In contrast, while sleep apnea can develop in childhood, it more often becomes a significant and progressive problem later in life. Only rare cases have been reported of narcolepsy arising as the consequence of such structural causes as brain tumors, brain infections and head injuries. Its onset sometimes follows stressful events, but such does not indicate that it is a psychological disorder. In fact, some breeds of dogs develop narcolepsy on a genetic basis. Narcolepsy may be complicated or complicated by emotional or physical problems rather than by narcolepsy, or that the patient may be malingering.