Demon possession was an ancient world's explanation for psychotic episodes in various mental illnesses. It's fear-based rather than fact-based.

My first wife was schizophrenic and for a short time was in thrall to an Assembly of God elder who did exorcisms. She obliged by throwing grown men around the room despite her slender build. But I can tell you that she had terrible muscle aches for days after doing so. Adrenaline is the explanation for this. I have a lot of not-so-nice things to say about my first wife but being demon-possessed isn't one of them. I put a stop to that crap. What she needed was mental health standard-of-care, such as it was. Too bad she refused to submit to it.

I've never had any problems with demons ever since I stopped believing in them. Before that I just wasn't too sure.