In my basic training company in the Army about fifty-four years ago, we had a fellow--think his name was Simpson--who was perpetually falling asleep.
We'd be in an outdoor training class, in bleachers, and the instructor, in full flight in his lecture, would STOP!--and Simpson! Wake up!"
And then, two or three minutes later, Simpson! Wake up! Stand, so you can stay awake!
A little later: Simpson! WAKE UP! Stand at attention!"
Sure enough, not too long later: SIMPSON! Get your rifle from the stack! PREE-sennt....Harms!!! And there, standing at attention, holding his 12-pound or so rifle stiffly in front of him, Simpson would drift off to sleep, and maintain that posture all the while!
It was truly amazing, under what circumstances Simpson could and would go to sleep. He was eventually given a medical discharge, and a good thing, too. I sure wouldn't have wanted to be in a combat unit, on the front lines, with him as one of my platoon-mates, whether day or night.