Do you know what else causes a cold feeling of dread? Carbon monoxide. You know, the stuff in car exhaust and natural gas leaks that can easily kill you? Apparently, lower doses of CO start the process by giving you the willies. You get nauseous and your body essentially senses that something is amiss. Unfortunately, many people assume their bodies are telling them supernatural secrets, when all it's really trying to say is, "Change the batteries in the CO detectors, dumbass!"
|"Sooner would be better!"|
Does that seem like a bit of a tenuous connection? How about this: later stages of carbon monoxide poisoning introduce awesome new symptoms like headaches, respiratory arrest, and visual or auditory hallucinations. Also death. That's an important one.
So to recap: people who report ghost sightings very commonly report feeling a sense of dread, then later seeing a terrifying apparition. Both of these events, in the correct chronological order, are symptoms of CO poisoning. Don't think I'm making this up, either. It's nothing new. Scientists and skeptics have been suggesting this explanation for ghost stories since 1921. The explanation just doesn't spread as easily as a ghost story would, because chemistry is boring and hard while ghosts are scary and awesome.
The second, and infinitely more terrifying (though less lethal) explanation, is your brain turning on you due to miscommunication. One common type of ghost sighting involves waking up utterly unable to move and sensing (or seeing) a dangerous presence in the room. This is a common enough story to have myths based on it.
The reason it happens? Well, basically, you woke up wrong. When you wake up at exactly the wrong part of a REM cycle, there's a chance that the part of your brain responsible for waking up your consciousness will partially function, while the part responsible for waking your motor functions will be caught unawares. Since your consciousness is only kind of awake, you still half-dream -- and since your brain is programmed to be alert to danger when you're vulnerable, your half-dreams tend to be nightmares.
The worst part? Being partly conscious can convince you, even after you're fully awake, that the whole experience was 100% real. So for the rest of your life, you could remember very clearly being visited by this: