One night when I was about thirteen, the temperature in my bedroom plummeted in seconds. Frightened, I hugged the blankets up to my chin, but my breath escaped out over them. The far corner of my mattress sagged, as if someone was sitting on it. The other end corner slumped too, then the blankets began to ripple with invisible snakes on a direct path toward me. My breath came faster, steam puffed out harder, until a twisted face of a ghost appeared through the haze, leering over me. ...