If you absolutely can't move, I would guess it's sleep paralysis. My college roomate a couple years ago suffered from narcolepsy, and she would often find herself unable to move any part of her body. It was very scary for her...but it happens occasionally to lots of people and it's nothing to worry about.
Don't worry about it!! I've had the same thing happen too.. It's so weird, you get a fear so you have to have someone around you and it feels weird to even lift so you use your other arm and just touch it until feeling comes back.. eghhg discomfort