A condition in which a person is unable to maintain alertness during the daytime hours, excessive daytime sleepiness (EDS) is characterized by a general lack of energy, even after apparently adequate night time sleep.
Naps can restore alertness, enhance performance, and reduce mistakes and accidents. A study by the U.S. National Aeronautics and Space Administration (NASA) on sleepy military pilots and astronauts found that a 40-minute nap improved performance by 34% and alertness by 100%.