Encountered probably the most annoying thing so far in Skyrim last night. I'm assuming the vampire stuff is all a part of the Dawnguard DLC. I finished up that main story line the night before. However, one of the side effects of dealing with Vampires is that you can potentially contract a disease which will turn you into one after a period of time. As long as you use a potion or shrine to cure it within a certain period of time, nothing happens. Once you get past that point, you become a vampire and start having effects like being weak against fire, the sun causes bad effects.. and you get thirsty for blood and have to feed.
Now, I have no desire to be a vampire, I'm just trying to play the GD game. At some point during my last battle in the DG quests, it told me I had contracted that disease, so I used a potion of cure disease, which is supposed to heal it. I didn't think anything further of it, but out of the blue, I start getting messages like "Your Vampire Blood boils in the sun" and crap like that. So I try using another potion... no dice. So somehow, it's claiming I'm a vampire. So I look up how to deal with that, and see that you have to talk to an innkeeper to start the quest to undo it. However, no useful options are happening. Eventually, I decide to try having Serena turn me into a Vampire Lord. Fortunately, this DOES trigger the quest to undo it and I think I'm rid of this crap now.