This is the first nightmare that I remember from childhood. It was one of those nightmares where you wake up screaming for somebody, a friendly face to prove that it wasn't real, that you really are safe in your room.
Probably what made it all the more frightening was the setting of the dream, which was indeed in my own room. From my bed I look up, and what I see is a two headed monster, conical pale faces with pale pink lips grinning maliciously, both heads bobbing back and forth. The creature's body is like a caterpillars, with ringed segments, though it has two human arms and stubby little legs at the bottom, and it is bouncing from side to side as it sings, "I'm going to eat you, I'm going to eat you, I'm going to get you and eat you up!"