It's a simple enough thing. It's all a part of the body's sleep processes. Sleep paralysis, right? No big deal, really. Your body produces a chemical that paralyzes your body during REM sleep to prevent you from hurting yourself by thrashing about during your dreams. No big deal.
Okay, so you opened your eyes and you can't move your body. It's the chemicals. Oh, you can keep trying to wriggle those toes, but it's not happening. Forget it. Just relax. It'll go away. It's fine. It's normal.
Oh, now there's something pressing on your chest, real hard. It's making it hard to breathe. It's heavy, so very heavy, whatever's on your chest. Chemicals. It's all chemicals. Stop trying to scream. It won't work. Your throat muscles are paralyzed, too. You still can't breathe.
You are staring at a blank ceiling. You can't stare anywhere else. Shadows flit across your vision, forming shapes you try not to think about. A clawed hand, a flash of jagged, shadowy teeth. All images from your subconscious. A face forming above yours, leering through black eyes.
You think you hear sibilant whispering. Angry hissing, like a snake that's been disturbed.
Suddenly, a sharp white light briefly flares in the room as a car pulls down the street, dispelling the shadows. The weight is gone. You can breathe, your hands clench sheets.
You feel an eternity has passed by but it was all the work of a moment. You wriggle, just to prove to yourself you can. You sit up, take a deep breath, and laugh a little at yourself. Sleep paralysis. Stupid.
You turn to shake your spouse awake, eager to share your experience. You feel paralyzed again, but it has nothing to do with sleep paralysis. You stare at the blood, the jagged wound in her throat, her wide, staring eyes, mouth opened in a soundless scream.
You survived your Old Hag Syndrome.