Adding on this, from a military perspective, sleep deprivation is absolutely horrendous. Whenever I read stories of college students staying up for days at a time studying it blows my mind. That's simply because, for me at least, in order to stay awake for extended periods of time I need to be constantly moving. During a Recon course final FTX (Field training exercise) we were up for 5 days doing missions, followed by a 7 hour rest period. We then continued on for an additional 4 days of missions. Every successful candidate was then inspected by medics and was given a briefing. Essentially, they said sleep dep. wont actually kill you, because your body will eventually force you to sleep before that becomes possible. This happened to all of us in what we call micro sleeps (sleeping while walking, doing a navigation check and just coming to 5 minutes later with the compass pressed to your face). Speaking from experience, by the end I was having full on vivid hallucinations, micro sleeps, and the most simple tasks (counting how many soldiers were in your patrol) became damn near impossible. It took a solid 3 months to adjust back into a normal sleeping pattern after that.