Eh, it gets warm, who knows what kind of shifts/day he had previous. Sometimes you don't choose for things to happen like that, they just do.
And if you do it in the Marine Corps you can go to jail, or worse... in a combat zone get all your buddies killed!
NOT an excuse.
Heck, I've been working longer hours than a 12 hour shift for MONTHS and haven't taken a nap, nor thought about using it as an excuse!