TB patients had very pale skin, red rimmed eyes, and coughed up blood.
mostly it was 2 things, sleep paralysis on sudden waking and the observation of continued hair and nail growth after death.
Sleep paralysis is when one wakes suddenly and the brain chemistry has not switched from sleep to waking and the persons body is still paralyzed by REM sleep, this was often accompanied by the feeling of something or someone pushing, lying or sitting on the chest, it is often called "the old Hag", the vampire idea came from folks brains trying frantically to "make sense" of the situation so often bizarre perceptions and dream fragments were confabulated to become an Incubus or Succubus.
The hair and nail growth is true, metabolism does not stop abruptly at death, so there is hair and nail growth for up to 2 weeks.
No,it started with Vlad the Impaler in Romania for what he did to his enemies in battle.his army put them on stakes and you could watch them slide down on them.Tons of blood were shed from his battles back in the 1400's.he built a castle so large that it was impossible to distroy.one woman 150 years before Bram Stoker wrote his novel,a woman who's name I can't remember her name,took her ideas from Vlad,and came out with,Varnnie the Vampire in your weekly Penny dreadful news paper.and then came Bram.
I think also misunderstood conditions(at the time) such as Albinism and Haemophilia added weight to such stories