Oddly enough, I wasn't really scared when I was with my housemates. I was pretty darn scared if I was on my own at night when it happened though!
Thing is that demons presumably want you to be terrified, the whole point of it is to unsettle you and make you afraid. Fear can be so crippling yet our rational mind can overcome it. It's good to remember that our guardian angel is always with us and there is nowhere on Earth where God is absent. No matter how much demons rage and attack, if we trust in God and stay in a state of grace they cannot harm our souls. I heard a pithy saying once "All the darkness in the world cannot put out the light of one candle."
Sleep paralysis is a scientific theory but not a proven fact as such. I don't know how much mileage there is in it- I do know that it can only be applied up to a point as it doesn't allow for the existence of the supernatural.