I hope 16 hours without sleep doesn't cause brain damage, because I've stayed up twice that long in the past! Medical interns often go 24 hours without sleep.
Not sleeping for five straight days probably wouldn't be good for you. 16 hours is a normal amount of time to be awake. You probably just feel crappy because you slept too much or not enough. Or you might be a little dehydrated, etc. You'll shake it off as the day goes on.