OMG. That's scary. I hate dreams in which I can't move something. I have read that it's because our muscles are actually paralyzed when we sleep. It's supposedly to keep us from hurting ourselves while we are sleeping. So when our legs won't move, that's why.
I used to have a recurring dream that I was trying to make an important phone call, but the phone was broken or the call would not go through and I would desperately try over and over. I haven't had one of those in awhile.