it's hard to explain but you've probably experienced it...
I was having a bad dream earlier. I think I was with friends and we were under attack in a war or something... and I realised I was awake, but still thought the dream was real.
And I was frozen...I actually couldn't move. And when you get in that situation you try to shout for help and you actually can't make a noise.
I hate it
eventually it subsided and I fell back asleep.