Towards the end of basic training, we were approaching a big field exercise. Our captain decided to put us to the test by subjecting us to a trying exercise.
I remember getting less than 12 hours of sleep in for a duration of 4.5 days. A couple of times, we'd set up camp - dig fox holes - prepare for rest, only to be awoken by a suggested-impending attack. Long marches, exercises and sleep deprivation put a fairly big strain on people.
I remember being unable to keep myself awake, unless I was doing something - and observed sergents falling asleep mid-sentence while instructing us recruits.
One lieutenant was caught sleep-walking out on a field.
We'd also start seeing things out of the corners of our eyes.
Sure; exams, gaming gone awry, jetlag, work and partying leads to 48h+ sleep deprivation from time to time - but the stress of military exercise mixed with sleep deprivation was an entirely different experience. Tolerance was at an all time low - and empathy for whining was virtually non-existing. You found yourself hating those that slowed progress, as you felt that they were extending the pain.
On a side note: While not exactly healthy - going into town to party, while sleep-deprived can yield some interesting results: I find myself less reserved, and more concerned with the immediate: There's less reflection - and more impulsive behavior.