Narcolepsy affects around 1 in 2,000 people. Experts estimate that around 135,000 - 200,000 Americans have narcolepsy, but the number may be higher. Only about 25% of people who have narcolepsy are actually diagnosed with the disorder. Patients are often mistakenly diagnosed with other conditions, such as psychiatric or emotional problems. Many patients wait decades before receiving a proper diagnosis.
Narcolepsy symptoms usually first appear in adolescence or young adulthood. However, narcolepsy can begin at any age. Growing evidence suggests that the disorder may emerge in early childhood in many patients. It can often be misdiagnosed as another disorder, such as ADHD or depression. People who develop it at a young age often have a family history of the disease and a severe condition, suggesting that genetic factors are important in this group.