I'm not sure exactly how long was my longest time without sleep, but I'm guessing around 30-40 hours. Not much, I know, but I did start hallucinating by the end. I didn't see anything, but I kept hearing short bursts of laughter and then someone would say my name behind me. Always in a different voice, and always in a voice I knew but hadn't heard in a long time. I probably started looking paranoid and jumpy at least. That was about 8 years ago, and I've never gone that long without sleep since. So, even a short amount of time can screw you up a bit.