The longest I've stayed awake was on a cocaine and drink fueled binge of 5 days and 4 nights. I frequently go for 2-3 days without sleep and although I do lose concentration and forget things easily, I have never hallucinated.

On the other side of the coin, when I was 12 years old I got Beijing Flu and slept for 13 days without waking up. My mum was a junkie and didn't take me to the doctor until afterwards. The doc said I should be dead! lol.