I've been there ... at least 10 times. :)
It doesn't help that my birthday usually falls on a long weekend. Then you justify it in your head. "I don't have to work on Monday, so I can keep drinking. It doesn't matter that I can't feel my face. Or maybe that's someone else's face... I don't have a moustache ... Why is there a moustache?"
Then, one of your mates brings you another drink and tells the dog to get off the couch.
Yep, thats about the size of it. I always take an extra day off for my birthday at the tail end of the weekend so I get a long one and it just means its one big shitpit of drunkenness and hangovers and they do tend to merge!