Shadow Figure attack. wtf ?!?!

Um... what was it and what to do about it. I awoke because i couldnt breathe. when i opened my eyes there was like this shadow figure ontop of me with hands over my mouth suffocating me. I was really scared i started swinging my arms and jumped up outta bed fell on the floor ran to the light turned it on and there was nothing there. Pretty much the scariest experience to ever happen to me. Truly frightening. Any and i mean ANY help advice would be greatly appreciated...