[muawiyah]

Nonsense. I made it through the US Army Infantry quite well with never falling asleep except during prescribed periods, or while riding around inside a multi-ton very noise tracked vehicle (where presumably that was allowed).

People unable to take advantage of such moments probably did get tired, but that's no excuse.

[Mr Rogers]

Exactly. There is no excuse for falling asleep on guard duty. If you try hard enough, you will stay awake.

Folks falling asleep on guard duty are not handicapped people we need sympathy for, but slackers. The very rare person who cannot stay awake gets weeded out before combat.