Franz Hartmann was a German vampirologist. He reported a story from the 1890s of an alcoholic man who was rejected by a woman whom he was in love with. When she rejected him, the stories say that he committed suicide by shooting himself.
Soon afterward, the woman began complaining of vampiric attacks from a specter in the form of a recently dead suitor. She could not see him but was aware of his presence.
Doctors diagnosed her as an hysteric but couldn’t do much to relieve her symptoms. After a person accepted her explanation of vampirism, the woman finally submitted herself to an exorcism by that person.
After the exorcism, the attacks stopped.
Today, many psychological theories shun the idea of vampirism, but explain the symptoms as guilt caused by the suitor’s suicide.