Nearly 48 hours.
At uni I'd been awake for 6 or 7 days (and spent a fortune on tea and red bull), went to sleep at 6pm on one day (let's say the 5th for simplicity) and didn't wake up until about 3 pm on the 7th. Skipping an entire day does weird, weird things to you, I was confused for the rest of the week.
Worst thing was waking up on the 7th, starving hungry, busting for the toilet (cleaners were in and couldn't get into the bathroom - ended up having to find a hedge outside) and I had the worst "dead legs" I have ever experienced, took about 4 hours to lose the "pins and needles" feeling.