When I was in the guard’s grave I made my way to the Abomination. While fighting it I somehow ended up on top of his head. This happened several times with other bosses so I wasn’t too concerned.
However, when it happened there I was unable to move so I couldn’t get down, and jumping made me go further up in the air. I could continue jumping in the same spot raising higher and higher into the air until I was looking down over the entire map.
Still couldn’t move though, so I had to re-log at which point I spent several minutes falling before finally hitting the ground.