You were drinking too much. You know that now. If you hadn't been drinking too much you wouldn't have made that foolish bet. Now it's too late.
The fellow looked so young, so inexperienced. He looked drunk, too. So when he bet you 500 gold pieces that he had a magic spell you couldn't get yourself out of, you naturally assumed he was bluffing.
He wasn't bluffing, and he wasn't drunk. You have awakened in an underground labyrinth. You feel tired and drawn. It's more than a hangover, though you certainly have one of those. No, it's as if a part of yourself were missing.
A part of yourself is missing!
You have been split into two selves, and what is worse, your other self is somewhere else in this maze. You cannot survive outside this magical maze unless you merge back with your other self.
Source: Eamon Wiki.