It's a cracking supernatural thriller with a killer twist, I quite agree. I'll have to rewatch it to catch all the clues you mention in this article (or better still, read on the book on which it is based, which I confess I have not done).

I dabble in the gothic mystery horror/thriller spectrum myself, sometimes with a supernatural edge. Here are some of my novels if you're interested, one of which concerns astral projection as well (The Thistlewood Curse). :)