Ok i was sleeping and then i woke up. But not instantly i just barely opened my eyes and then after that i couldnt move. And also i kept hearing things.I was scared because i didnt know what was going on. And i also felt like i coulndt breath. Like a minute later i could move again, but i couldnt go back to sleep. I was so paranoid and scared of what happend. I thought i was going to die.

Can someone please tell me what this is.?
And also why it happens.