I went through something similar to what you describe. My solution was to confront it head on. I turned the light off. Waited for the ghost/monster/whatever. Nothing.
Also went into cemeteries at night. Nothing. I eventually came to love the night.
There are no monsters. There may be ghosts but I've never seen or felt one and I've been in some places that you would think ghosts might be present if they exist.
I think your mind conjuring up frightening images may very well be anxiety.