What is shell shock?
Shell shock
is a term coined in World War I to describe the type of posttraumatic stress disorder many soldiers were afflicted with during the war
Shell shock is a term coined in World War I to describe the type of posttraumatic stress disorder many soldiers were afflicted with during the war (before PTSD itself was a term).[2]  
It is a reaction to the intensity of the bombardment and fighting that produced a helplessness appearing variously as panic and being scared, flight, or an inability to reason, sleep, walk or talk.[3]