Seán Manchester (from his writings) on psychic vampirism:
Individuals who seem to drain the energy of those around them have probably been experienced by many people, myself included, but here we are employing the word "vampire" as an adjective.
Experiencing such energy-drainers is nowhere near the same as a predatory demonic entity masquerading as a dead person; though I recall an old lady who ran an antiquarian bookshop in north London many years ago telling me about her encounter with Aleister Crowley as he passed her on the shop's stairs and how she immediately felt faint and nauseous. Was this Crowley draining her of energy? Or was it his extraordinary notoriety effecting how she felt? She claimed the former. I suspect the latter. But we will never know.
So-called "psychic vampires," or "psi-vampyres" as they sometimes like to call themselves, claim to lack an adequate energy system, and this inadequacy compels them to feed upon and tap into the energy and vitality of other unsuspecting host victims. This allegedly results in a temporary surge of energy in the "psychic vampire" and a serious loss of physical and mental energy for the "prey."
Victims attacked by "psychic vampires" have reported to have felt depleted both mentally and emotionally. The more unfortunate victims suffer from a prolonged loss of energy and permanent damage to their general health and vitality. In certain severe cases it is claimed the prey might even suffer from very serious illness after having such an encounter. I cannot say I have witnessed anything of this sort. That notwithstanding, I have been aware of a small number of people who appear to be draining on one's energy when in their presence. Yet I suspect we have all experienced this at some time without necessarily attributing it to "psychic vampirism."