Dee has a good point. Parties are for fun and right now you are not having fun but are struggling and if you pick up to join the crowd, it won't be fun tomorrow when you beat yourself up and have to start at day one again (that is if you don't just keep drinking).
Tell them you have to go (headache is a good excuse) and bail....make sure to get yourself a big slice of chocolate cake as a reward for being so good
and call your sponsor.
Oh shoot...just read your post about the boss.