The longest I've ever stayed awake is 4 days, so roughly 96 hours. I did it back in high school. I don't really know why, I just remember I didn't feel like going to bed, and for some reason that feeling lasted four days. I don't remember much of it. My friends have told me bits and pieces of what happened: around day two I was really loopy and annoying, day three I was very cranky and irritable, and day four I was more or less a zombie (apparently I tried to bite someone). After that I finally went to sleep, and stayed asleep for two days.
Right now I'm running on being awake for about 26 hours. I'm going to bed sooner or later. I can't stay up for almost half a week like I used to.