Hallucinations caused by carbon monoxide poisoning from gas lamps in the house, cooking fires, coal boilers, what have you. All the same symptoms of ghost sightings are consistent with varying levels of CO poisoning.
If there were ghosts, even good ones, my grandfather would have visited me in the house where he died and I lived for 4 years. He visited my grandmother in her dreams. Never when she was awake, get it?
