Sofageorge is correct.
There was a guy doing a sponsored radio broadcastathon that meant he stayed awake for two weeks. The guy was irreversibly changed, his wife said he was never the same again.
It's down to the lack of REM sleep. It's the only sleep you need to have. Well, that's not particularly true but REM is the essential one to have.
You need this point of time to let your body process the days events, you can only go without REM for so long before it adversley affects you and stress levels rise, along with blood pressure etc....
There was a case somewhere that a guy didn't sleep for 6 months due to a brain condition... he died, his body just gave up.
Generally though you'll be okay, 5 days is extreme but unless your body isn't sleeping due to disease for example and the brain is working properly you'll go into auto shutdown and have to sleep. Rem sleep usually comes about after 2 hours but if deprived enough and you enter it in 10 minutes.
That's about all I remember from A level Psychology.