I’ve long held a hypothesis that a lot of folklore monsters are based on prejudices and stereotypes against behaviorally divergent people. While this post references autism, I feel like the origin of vampire myths are most likely rooted in what are essentially nasty rumors about people that regularly engaged in behaviors that would eventually become associated with OCD (and ironically, I would argue that almost all of the behaviors described in this post besides the sleep schedule one are much more associated with OCD than autism).
For instance, a common OCD thought pattern is being intensely preoccupied with how strangers perceive you, which leads you to engaging in agoraphobic tendencies, which could easily lead to people coming up with wild and cruel speculation about why you might struggle to be outside like everybody else
People with OCD might compulsively avoid certain foods and become intensely distressed if they are exposed to the foods they’re avoiding, like a vampire trying to avoid eating garlic.
Compulsive rituals is another one. This is literally just OCD in the most obvious sense. There’s an old legend that you should bury a vampire in rice because they have to count every single grain any time they find it.
And lastly, another extremely common OCD thought pattern involves being intensely preoccupied with concepts like blasphemy and sacrilege and religious imagery in general, and I think it’s easy to see how that sort of issue can lead to people, especially along time ago thinking that you are some kind of unholy individual.