So I did something or other and now I am a vampire.

Not sure if I got bit, whacked with something or what, but I was normal, I fought some vampires killed them all, slept in their dump of a home and now I am one.

A: They were all dead so how'd they get me when I was asleep?

B: Surely something like this should have a unique sequence showing me getting bit or something?

C: I can't think of a C.

Why even have Vampires if there is no quest and they are not going to milk the experience or anything . Its like a token feature throw in for no reason.

Stuff like this needs polishing up a bit.

vampirism is a diseas in Elder scroll, you contract it possibly when you take hits and then it turns into full on vampirism.
Edit; to clarify at first its a curable diseas but after a time (when you slept) it turns into full blown vampirism.