We've all been there. You're half asleep, the lights may not be on yet, and you see a shape out of the corner of your eye.
In a horror movie, it would be a ghost or a serial killer about to attack, but in real life we just end up with a tiny heart attack. If we're lucky, it passes in a moment. If not, we squeal loudly and anyone within earshot will never let us live down the embarrassment.