In order to join the military you need to qualify medically. And while there are some obvious stipulations, like the fact that you can’t be carrying diseases that will endanger your platoon, there are other disqualifying conditions that might surprise you.
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.