I don't know if you ever watch "Paranormal State" on A&E, but Monday night they aired an episode in which a woman was plagued by a supernatural entity that caused pressure in the head, nausea, and dizziness. The psychic they brought in could pick up nothing in the way of spirit activity. Further examination revealed that the house was haunted by, you guessed it, a CO leak from the furnace flue. Kind of an anticlimax, but it provided a good opportunity for the crew to air a warning about the risks of CO poisoning.