[split] Vampires and Vampirism

[Apricots]

Why are humans that turn vampire often portrayed as changing personality completely? Going from pretty calm persons to raving monsters? Changing priorities makes sense, like that they have a tendency to find human blood irresistible... slight changes in personality, like traits becoming more pronounced, ok. Going directly from whatever they were before to monsters whose only resemblance to former selves is physical... that makes no sense.

I suppose it's sort of following on from werewolf legends, where people both turn into werewolves and take on the trait of the werewolf to become raving lunatics. Remus Lupin in Harry Potter, for example, who could only be calmed by wolfsbane potion. It's a fairly common trope to change personality when you change your physical self, I think.