I work in a nightclub and routinely only get 4-5 hours of sleep. A couple of weeks ago I had work til 5:30am, got up at 9 to go house hunting, worked again the next tight til 6:30-7:00, took my girlfriend to the airport at 10:00, went home, didn't go to bed until my normal bed time that night (usually around 12:00 - 1:00). You can go several days without long periods of sleep, provided you still get REM sleep in that time. There is nothing worse than sleep dep, except perhaps gassing out.