stay up for 24hours before you even think of dropping, and rest assured - eventually sleep will take the tripper. having a buzz on a stimulant drug the night before a trip can also make for the need for sleep.
i fall asleep at some point during almost every trip. though i usualy awake suddenly shortly after falling asleep. my dreams are always very vivid and weird. i always have a hard time telling if my dream was real or a dream.
on my sister's birthday last year we tripped together at the beach. we both had four hits which we tore into halves and took every thirty minutes. we did this at about 1oclockpm, and we were still tripping at five in the morning. We went up stairs to try and sleep, and she couldnt sleep at all and just read. But I lied down to try and sleep, because I was freaked out that I still couldnt count to five without getting lost by the time I got to three. I dont remember falling asleep at all, but I remember waking up, not knowing I was sleeping. I woke up having heart palpitations, trouble breathing: a total panic attack as a result from an interrupted "trip dream". my sister said I slept for about 10 minutes, because she was listening to my breathing patterns
i can never fall asleep on acid. if i take my dose at nights its guaranteed for me that ill be up to dawn, but watching the sun come up on while i lay on my roof is extremely fun at the tail end of a good trip so its a worthy trade off.
I was in the 10-12 hour range back in the day. I'd never take it after 9pm. Hated trying to sleep on it the next morning.
I'm sure it is possible to fall asleep on it, but when I did it, I took it around mid day, and I didn't fall asleep until 6 A.M. I went to bed at 3 A.M. I just spent three hours laying in bed tripping balls, listening to music, and trying to use the computer.