I'm always curious about this, about people who say they routinely sleep < 6 hours a night. Now, I know there are some very small percentage of people who, genetically, need very little sleep, but for the vast majority of humans, I don't think this is really physically possible.
I can certainly pull an all nighter once in a blue moon, or go two nights on a couple hours of sleep. But honestly, I feel like total shit after a single night with less than 6 hours of sleep, and if I do this more than a night or two in a row I always get sick and I can barely think straight. I honestly think I would die or at the very least end up in the hospital if I was continually on 5 hours of sleep a night.
I know I need more sleep than most people (I'm fine on 8 hours but my "natural" preference, e.g. with no alarm clock, is 9), but I always wonder about people who say they go months on 5 hours of sleep a night. I always think they're either superhuman or exaggerating their sleep loss.