Teiresias: Seems I was wearing a cursed item I picked up in the Ice Caverns (had to look it up since the description didn't tell me, and I'm not sure if a high enough lore skill even tells you that). However, according to everything I read cursed items are only supposed to drop your health when you go up or down a level or go to a new world, but I was getting constant drops just walking around.
In any case, I went to an earlier save game where it wasn't happening (luckily I had one even though I lost a bit of progress) and it hasn't happened since. I'm starting to wonder if the game glitched and thought I was constantly hitting a wall while jumping since I had lost quite a bit of health doing that right before it started. I do think that's a stupid mechanic giving how horrible the jump control is in this game.
Anyway, at least it's fixed now. Thanks everyone!
In my experience, a cursed item triggers whenever you have some sort of state change, which I believe includes picking items up, dropping them, and moving items around your inventory. I think you can carry a cursed item without problems, but wearing it is a bad idea. That's been my experience, mostly from UW1. However, I haven't done much testing on it because ow.
I think you can identify an item as cursed if you roll high enough on your Lore check. Also, just removing it and dropping it should stop the cursed item from continuing to damage you.