I started again and realised what I did wrong. It's nothing to do with the Gnome quest, it was because I got trained in the Doctor skill tree. The second that I did that, I started being "healed" which prompted my health to show -21463533 (or something like that). And you cannot reverse that either, only options are to restart from scratch or reload an earlier save. I just didn't bother getting those skills....especially seeing as I had Infinite Health!!