Punk661, this is one of the most common types of questions I receive -- and that's not surprising because this phenomenon is very common. It is not paranormal, but is a condition known as sleep paralysis. Most people experience it occasionally, and some people experience it more often. I've had it a few times myself, and it is a very scary and often frustrating experience. It is often accompanied by the feeling that you are being watched or that there is someone else in the room when there might not be.

According to an article in About.com's Sleep Disorders section, "episodes of paralysis can occur when the body is in any position, but happen most frequently when the sleeper is lying flat on his or her back. Intense fear is common, but sometimes other strong emotions, such as sadness or anger, are present. Often a sensation of pressure on the chest makes it difficult to breathe." That feeling of pressure is what gave rise to the myth of Old Hag Syndrome, the archaic notion that an old woman's spirit was sitting on your chest during your sleep.

What's the solution? The Sleep Disorder article says, "The best remedy is to will yourself to move, even if it's only the wiggling of your little finger. This is often sufficient to break the spell. If you can manage, it, scream! Your roommate may not appreciate it, but it's better than suffering through a long and fear-filled episode. If all else fails, seek professional help. There are drugs that can help you."