The power of the imagination is an incredible thing. I don't have any doubt people see, hear, and feel "ghosts", but the reality of undead spirits floating around effing with people is HIGHLY questionable to me. As far as I'm concerned, it's all in your head.
The problem with your line of reasoning is that the spirits are not floating around effing with people. They exist on another plane and are only carrying on the way they do. There just happens to be moments where our physical plane crosses over with the spiritual.
