You wake up in the middle of the night with a heavy weight on your chest. You can’t breathe or move. You feel a presence in the room, studying you. You want to touch it, or move it, but your arms are pinned. You can feel its hot breath on your cheeks.
Option 1: You have become the prey of an incubus or succubus. It is slowly draining the life from your body. However, you may enjoy the sex before your soul is sucked out of you, so that’s something.
Option 2: You have awakened into a hypnopompic state. Your body is suffering the kind of paralysis that is normal when you are sleeping but deeply frightening when your mind is awake. This unusual condition may result in your panicked mind misinterpreting local external stimuli: demons; possession; aliens at the foot of the bed; succubi; magic. It is terrifying, but an explicable medical phenomenon.
Option 3: You own a cat.