None of the major symptoms of narcolepsy are exclusive to it. Excessive daytime sleepiness, the most common of all narcolepsy symptoms, can result from a wide range of medical conditions, including:
- Other sleep disorders, such as sleep apnea
- Various viral or bacterial infections
- Mood disorders such as depression
- Painful chronic illnesses that disrupt normal sleep patterns, such as congestive heart failure and rheumatoid arthritis.
Various medications can also lead to excessive daytime sleepiness, as can consumption of caffeine, alcohol, and nicotine. Finally, sleep deprivation has become one of the most common causes of excessive daytime sleepiness among Americans.
The number of conditions that share some symptoms with narcolepsy greatly increases the difficulty of arriving at an accurate narcolepsy diagnosis based on symptoms alone. Thus, the tests explained here are usually needed to make a definitive diagnosis.