Kinda sounds like a line out of The Godfather. Made men with fangs. The answer to this question, in practical terms, is pretty much like the sex talk from hell with your mother.
- A dog or a cat jumped over your body after you died. (Look, I didn’t say they were good theories, I’m just giving you the list.)
- You’re a witch and you didn’t do what the Catholic Church told you to do, so you die and go all bloodsucker. (Which confuses the hell out of me, because how is that damnation when your “go to hell” ticket is already punched for the witchcraft thing?)
- You commit suicide.
- You’re possessed by a demon.
- You’re a fallen angel. (Little case of grandiosity there, dead dude?)
Frankly, I think all of those are pretty freaking silly. I’m going with:
- You’ve been bitten by a vampire.
- A vampire swapped some blood with you.
- A half-human half-vampire: your folks did the nasty and figured the vamp’s little swimmers were no good. That’s usually how it works, male vamp / female human. The vamp just has to feed first to get his, systems going.