Activity

Show a person a random inkblot, and he’s going to bend over backwards to see a human face in it, or a human figure of some kind.  It’s the way our brains are put together.  When see an ambiguous stimulus, we automatically try to impose some kind of order onto it.  Human beings have a remarkable gift for imagination in that regard, and it doesn’t surprise me a bit that with just a little nudging, someone could imagine  full-blown ghost.  I’m just saying your original supposition — lying, hallucinating or seeing ghosts — isn’t quite complete, unless you count seeing a face in a cloud as a hallucination.