On reflection, maybe I got confused with the number of days you can go without water (also 7, at least according to my memory). I stayed awake for 5 days once and there was only a bare minimum of hallucination at the end. I could have stayed awake longer, it wasn't really hard by that point. The people I've known who stayed up forever on crystal meth typically started hallucinating after a week. I'm surprised that the limit is so much shorter, but I'll believe it, thanks for the link.