When you've done a few, and get used to them, the next day isn't actually too bad... I usually find that I feel fairly good in the morning after a coffee and shower, and only towards the end of the day do I start to flake... try go for a second, and then that's when things start to get dicey, falling asleep at the table etc...
First time doing it, you're gonna be knackered, and depending on how much you usually sleep, you're probably gonna find it quite hard to get through the whole night.
Keep yourself active and in a bright place to help keep yourself up!
luciie - we need an update on how you feel!
And actually passed?