Scientists argue

Whence came the people the belief in vampires? Probably, from the junction of essentially different factors, such as "energy vampirism" (celebrated psychologists phenomenon of the ability of one person seemed to take away the energy of another) and individual cases of mental disorders, when maniac really
drinks the blood of his victim. On the other hand, belief in vampires could cause fear
before darkness, insomnia, hallucinations. The belief that the propensity to vampirism
transmitted by the bite, and could determine the very real human rabies
and animals. However, all these completely rational reasons not explain why
belief in vampires made known in the Balkans and the Carpathians. Remains
suggest that they actually somehow were performed there.

Aleksandr Levchuk