1) I'm very sensitive of lack of sleep, and so I take having 8-hours or more of good sleep extremely seriously. 2) Most days I don't have any sudden sleep syndrome. 3) I've had cases of sudden extreme sleepiness for no particular reason since I was a child. The only thing in common I can think of in this cases is being indoors.

I never thought about it before, but I might have a case of narcolepsy or something similar.