Why am i paralyzed in my dreams! its creepy..?

okay, i have been having this dream where i cant talk/yell/ and move. i feel something evil is around me, WHY IS THAT. i get this heavy feel in my chest and i cant breathe well. ((physically im healthy)) i have this dream SO often its not even funny. it feels as though im being absorbed into something. and also something screams in my ear soo loud it feaks me out. i cant move and i know im not dreaming or it seems like it. whenever this happens i feel like something evil is around me trying to kill me, other times it feels like god is talking to me, and other times it seems like something is calling out for help. ((the yelling sound i hear)) it freaks me out so bad. I know im not the only one hvaing this kind of dreams becuz i know some people had them too. I heard this is some kind of evil spirit thing. IS THAT TRUE!?! Becuz if it is, thats going to freak me out. I hate having this experience, its one of the worst experience you can get. I have it soo often this days its scary. How do i prevent this? i tried talking to god, and saying the lords prayer but sometimes it doesnt help. what do i doo!! what the cause of this. Why am i hearing this yelling sound! also it feels like im awake when im really sleeping. its like your sleeping but really your not.!!!