It's kind of interesting how people cope differently with lack of sleep. I was awake for about 100 hours straight last summer finishing my thesis, and after about 24 hours awake, I started to really feel it, but the worst was around 50 hours awake. Once I got to about 60-70 hours awake, I no longer felt any more tired than before. It was like I'd hit a plateau. And then I slept for 24 hours.