Physical causes
2015 research by Johns Hopkins University has found that the brain tissue of combat veterans who have been exposed to improvised explosive devices (IEDs) exhibit a pattern of injury in the areas responsible for decision making, memory and reasoning. This evidence has led the researchers to conclude that shell shock may not only be a psychological disorder, since the symptoms exhibited by affected individuals from the First World War are very similar to these injuries. Immense pressure changes are involved in shell shock. Even mild changes in air pressure from weather have been linked to changes in behavior.There is also evidence to suggest that the type of warfare faced by soldiers would affect the probability of shell shock symptoms developing. First-hand reports from medical doctors at the time note that rates of such conditions decreased once the war was mobilized again during the 1918 German offensive, following the 1916–1917 period where the highest rates of shell shock can be found. This could suggest that it was trench warfare, and the experience of siege warfare specifically, that led to the development of these symptoms. Cowardice
Some men with shell shock were put on trial, and even executed, for military crimes including desertion and cowardice. While it was recognised that the stresses of war could cause men to break down, a lasting episode was likely to be seen as symptomatic of an underlying lack of character.
Shell shock is a term coined in World War I by the British psychologist Charles Samuel Myers to describe the type of post-traumatic stress disorder (PTSD) many soldiers were afflicted with during the war (before PTSD was termed). 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.During the war, the concept of shell shock was ill-defined. Cases of "shell shock" could be interpreted as either a physical or psychological injury, or as a lack of moral fibre. The term shell shock is still used by the United States’ Department of Veterans Affairs to describe certain parts of PTSD, but mostly it has entered into memory, and it is often identified as the signature injury of the war. In World War II and thereafter, diagnosis of "shell shock" was replaced by that of combat stress reaction, a similar but not identical response to the trauma of warfare and bombardment. Origin
During the early stages of World War I in 1914, soldiers from the British Expeditionary Force began to report medical symptoms after combat, including tinnitus, amnesia, headaches, dizziness, tremors, and hypersensitivity to noise. While these symptoms resembled those that would be expected after a physical wound to the brain, many of those reporting sick showed no signs of head wounds.