See ghosts? There may be a medical reason

Spooky footsteps, faint figures, the feeling of being watched – these unsettling signs of a ghost are as familiar to us as the goose bumps on the back of our arm (or neck).

But are there physiological explanations for those things that go bump in the night? ...

“ghosts” are often the result of pranks, environmental phenomenon, or physiological conditions such as sleep paralysis and the hypnogogic and hypnopompic hallucinations that accompany it.

Carbon monoxide poisoning – and the hallucinations that can occur with it – is another possible explanation, although Nickell says he’s never encountered this scenario.

... In 1921, the American Journal of Ophthalmology published a case study involving a couple who moved into a house and promptly began to suffer headaches, listlessness and strange auditory and visual hallucinations (footsteps, mysterious figures, strange sensations, etc.). Their symptoms were finally traced to a faulty furnace.

A more recent case in 2005 involved a woman who was found delirious and hyperventilating after seeing a “ghost” while taking a shower; respondents discovered a new gas water heater had been improperly installed, flooding her house with carbon monoxide. ...

via See ghosts? There may be a medical reason - The Body Odd - msnbc.com.