How do you remove the Level drain this nasty vampire just handed me

The cleric spell lesser restoration (or greater restoration, but that's level seven) gets rid of it. You can also get it removed at a temple or buy a restoration scroll, which any class can cast.

Any "restoration" spells will do, which can be purchased at temples or cast by your priests.
And you can also kill and resurrect your character, obviously won't work on the protagonist though......

Thanks for the fasy info, I feel really dumb now