I would direct you to the book A War of Nerves which covers these issues.

There were unquestionably many WW1 veterans, who continued to exhibit signs of mental illness suffered in battle. Roald Dahl tells a story of one of his teachers who had a severe twitch: it was explained to the children that an explosion had occurred that caused him to jump, and he was still jumping. There were much more extensive social structures to 'place' veterans in the 20s, even if they were not treated sensitively.

The effects of battle fatigue on the Vietnam veterans was given far more publicity because of the growth of pop psychology and psychology in general, with PTSD developed in the early 70s as a sort of compromise diagnosis which made the issue easier to deal with and treat. The mentally-damaged Vietnam veteran became a movie staple, either overtly (Rambo, Uncommon Valor, Deer Hunter) or just to toughen up the image of a cop or criminal.