On the other hand, doctors define EDS as the "inability to stay awake and alert during the major waking episodes of the day," Dr. Hollinghaus says. This means you go through periods of having an "irrepressible need" to sleep, and accidental lapses into sleep or drowsiness while you're at work or driving, for example. But a person can be very tired and fatigued and not actually dozing off, Dr. Hollinghause says. Or you may not even be able to fall asleep if you do try to nap . So simply feeling like you want to sleep all the time isn't enough to count as EDS — you have to actually need to be sleeping at inappropriate times during the day to qualify.