re: Possession (1981) l Now Streaming on Shudder

I watched this shortly after it was posted here. Watched the whole thing taking a few breaks as it went. You have to realize that just about everything you’re witnessing is a metaphor and the horror elements are meant to give you similar feelings of being in or a witness to a toxic relationship. And even if you’ve never experienced one before it will take you there. I can’t say whether it was a good film or bad. It was just something I experienced. And I think the director’s goal was to make you uncomfortable and he succeeded in that. Those feelings will either be new or all too familiar depending on how the relationships in your life after gone.

This was the best explainer I found.
This is Barry website