The vampires of folklore were usually described as one of two appearances- vampires that seemed to be physically there, and apparitions, or phantoms. Physically solid vampires were
actually reported less often than their phantom brethren...
The phantom-like vampire will feed on people when they are in bed at night. The vampire is often recognized as a deceased
neighbor, friend, or family member by the victim, after the vampire removes itself. It's physical appearance, other than
familiar resemblance to the victim, varies from account to account. Often, it is described as a dark form, with its features apparent only seconds before the attack. Other accounts state that, though transparent, was instantly recognized by the victim from the moment they saw it.
Though the descriptions are stretched far and wide around the world, the more recent spectral vampire attack descriptions
indicate that the victims very rarely recognize their assailants. Most of the time, these types of vampires are described as
a dark mass, occasionally described with glowing eyes.
"The fact that fewer eyewitnesses of the above type of creature in the past hundred years indicates that there is a severe shift in popular beliefs...Fewer people today believe that the dead can rise to harm the living. In the past, however, the belief was strong and could possibly be the reason that a supernatural assailant would quickly assume the features of the deceased."
(my sum up of the information in Konstantinos' "Vampires: The Occult Truth"...
You can read up more of what I posted here.
