Don't take it literally! Else, your ear might hurt... It simply means "to take a nap" or "to go to sleep", in the sense that you lie down on your side (which implies that your head will rest on either one of your ears). Thus, "hauen" refers to your ear's hitting the pillow. :D

Danke Julia :)

And if you make for example a correct guess then „you have hit the nail on the head“ - „du hast den Nagel auf den Kopf getroffen“, you guessed absolutely correctly.