Daytime sleep inertia in narcolepsy-cataplexy.

Eight volunteers with narcolepsy-cataplexy participated in a study of scheduled naps and performance. Sleep inertia was examined following five "short" naps of 5% and a single "long" nap of 25% of total 24-hour sleep time as determined by prior sleep log data. Contrary to some subjective reports, short naps (mean duration of just under 30 minutes) were accompanied by sleep inertia in narcoleptics. As measured by the descending subtraction task, this sleep inertia was at times quite prolonged and lasted 20 minutes after waking from midday short naps, which ended on average at 1555 hours. In addition, sleep inertia, as measured by both the descending subtraction task and the four-choice reaction-time test, was evident throughout both afternoon and evening short naps; however, it was completely absent from reaction-time test results immediately following the single long nap, which ended on average at 1640 hours. Sleep inertia was maximum after slow-wave sleep arousals and was minimal or absent following the first short nap, which also contained the highest amount of rapid eye movement sleep of all naps.