This is how you sign Nightmare in American Sign Language.

How to sign

To sign "Nightmare" in American Sign Language (ASL), make a flat "5" handshape with both hands, place the fingertips of your dominant hand against your lips. Move your hand away from your mouth. Rotate your hand so that the palm is facing downward as you move it down to your non-dominant palm. Then, place the tip of your dominant index finger near your temple and move it outward from your head while wiggling your index finger slightly.