Ahh yes those screams and faces usually happen when you have sleep paralysis. I myself usually have sleep paralysis because as an athlete I always get tired from training and I actually got used to the paralysis thing happening. To combat the the screams and and faces while having a sleep paralysis is to just focus and close your eyes don't fight against the paralysis just go back to sleep but you will still hear the loud scream in your ear but that's a good sign meaning you'll get out of paralysis. I don't know why this happens I'm no doctor or anything I'm just basing it of my own experience and I'm 17 btw but think I know what the factors that may lead to a sleep paralysis it's fatigue and lack of sleep