Hi Tizzee
First thing is a hug. ((( HUG ))) I know how freaky this is. This happens to a lot of people. It is called Sleep paralysis. Really!
http://en.wikipedia.org/wiki/Sleep_paralysis
Everyones experience is different, yet the same. You don't feel like you have gone to sleep yet and are convinced this is Not a just a dream, but really happening. You feel pinned to the bed unable to move, unable to scream. It feels like someone is in the room with you... it feels dark and sinister... all of the things you have written here...
Here are just a few of the links here at Mystic Board where others have shared their stories asking for help or understanding. I hope you get something positive for yourself so you don't continue to feel like you are being attacked by something unknown. This is an awful place to be in ones mind.
P E A C E
Evie