Feature of narcolepsy
The hallmark of this disorder is decreased REM latency, i.e. decreased latent period before the first REM period occurs. Normal REM latency is 90-100 minutes. In narcolepsy, REM-sleep usually occurs within 10 minutes of the onset of sleep. The common age of onset is 15-25 years, with usually a stable course throughout life. Ref: A Sho Textbook of Psychiatry, Niraj Ahuja, 7th Edition, pg. no. 138