During my last week of basic training, several Army Reserve drill sergeants arrived as pinch hitters for our regular instructors, who by that time probably wanted to kill us all in our sleep. These drill sergeants were slightly less tightly wound than our regular noncommissioned officers, and engaged us in small talk as we cleaned our weapons for hours and hours.
Benjamin Franklin nailed it when he said, "Fatigue is the best pillow." True story, Benny. There's nothing like pushing your body so far past exhaustion that you'd willingly, even longingly, take a nap on a concrete slab.