A condition usually found in Soldiers, where a traumatic experience forces the person into a state of shock, such as being in the proximity of an exploding Artillery shell (Hence Shellshock). They are quite often rendered completely incapacitated without suffering any physical damage. This is also often confused with PTSD.
The Marine began to run across the pitted sand, when the Howitzer shell hit next to him. He was launched into the air, and when he landed, he lay stiff as a board, on the verge of sobbing, he had been shellshocked.