Waking up and being paralyzed?

I have been waking up in the night fully awake and i can't move at all. My eyes are the only things that can move, but sometime i can't open them. Last night i had the same experience, but my eyes were open and I couldn't breathe and saw some figure by my bed and then on top of me. It frightened me a lot so i screamed, but no sound came out of my mouth. What is wrong with me?