clipped from: www.newscientist.com   
If you have been awake for 21 hours straight, your abilities are equivalent to someone who is legally drunk
SKIMPING on sleep does awful things to your brain.
Sleep is when your brain processes new memories, practises and hones new skills - and even solves problems.

There is also some evidence that sleep can help produce moments of problem-solving insight. The famous story about the Russian chemist Dmitri Mendeleev suddenly "getting" the periodic table in a dream after a day spent struggling with the problem is probably true. It seems that sleep somehow allows the brain to juggle new memories to produce flashes of creative insight. So if you want to have a eureka moment, stop racking your brains and get your head down.