It was not until World War I that specific clinical syndromes came to be associated with combat duty. In prior wars, it was assumed that such casualties were merely manifestations of poor discipline and cowardice. However, with the protracted artillery barrages commonplace during "The Great War," the concept evolved that the high air pressure of the exploding shells caused actual physiological damage, precipitating the numerous symptoms that were subsequently labeled "shell shock." By the end …showed first 75 words of 4077 total…

…showed last 75 words of 4077 total…believe. Many veterans report flashback episodes that last only a few seconds. For many, the sound of a helicopter flying overhead is a cue to forget reality for a few seconds and remember Vietnam, reexperiencing feelings they had there. It is especially troublesome for those veterans who are still "numb" and specifically attempting to avoid these feelings. For others, it is just a constant reminder of their time in Vietnam, something they will never forget.