"Narcolepsy is a disorder that affects many different areas of life. So in typical patients with narcolepsy, they have something called "excessive daytime sleepiness." So, they're very sleepy during the day. Yet, at night, they're still sleepy, but their sleep is very broken."
Source : "Black Swan Choreographer Benjamin Millepied on Teaching Natalie Portman to Have Swan Arms" by Rebecca Milzoff, www.vulture.com. December 3, 2010.