This is one aspect of extreme sleep deprivation. Having just woken up from my Sleeping Beauty-like episode after midterms (and staying up three days and two nights in a row), I feel obligated to mention the negative aspects. As long as things are actively going on, you'll be fine - sort of.
Walking to class, thinking and talking about concepts and facts I had no problems staying awake; coffee was my bitter friend, after all. But on day three it turned harsh. Waiting for a solution to cool in an ice bath, I found myself falling asleep three times while standing up. Furthermore, I started halucinating (if you care to call it that). My vision dropped to about seven frames per second when looking at fast motion (centrifuge) and I had the strong feeling that something (motionless) was going on in the corner of my eyes.
More coffee. Still have half a CS assignment to code
Mike was supposed to score me an eigth of KB for whenever this fiasco was done, so I keep AIM open. Ah, the window blinked. Wait. No message. Odd. Back to coding. Again, the window blinks without being updated. Fearing instability, I save and reboot. Same thing. The window is blinking sporadically - whenever I'm not focusing on it. I close AIM and hurry up to finish the assignment, wondering what is to come.
At one AM on the third day I'm done. I upload the assignment, grab my toothbrush and head off to the communal bathrooms. Brushing my teeth I see them... disassociated motions, movements without physical objects behind them in the corner of my eye. In the dark hallway... I feel a cold breeze in my neck, although there is no one else in the room.
I finally got to sleep after this, remembering it as something I want to avoid at all costs in the future. There is something impulsively scary about reality turning into a bad trip, the coffee reminding you that this is the most sober you will ever get... it's a taste of insanity even fifteen hours of sleep won't cover up.