Their method is to try first to cast their influence upon a man; then they enter slowly into his atmosphere and in the end may get complete possession of him, driving out entirely the real human soul and personality. These creatures, when in possession of an earthly body, may have the human appearance but they have not a human nature. Their habit is to draw upon the life-force of human beings; they attack and capture vital power wherever they can and feed upon it. If they come into your atmosphere, you suddenly feel depressed and exhausted; if you are near them for some time you fall sick; if you live with one of them, it may kill you.
https://veilofreality.com/2011/04/18/organic-portals-soulless-humans/