This is certainly a part of it. Also, a fear of nuclear war the likes of which hasn't been experienced by anyone who came of age after Gorbachev. Also, veterans of WWI, WWII, and Vietnam coming home fucked up for generations, with Gen X being the first to grow up understanding what PTSD is
those previous generations had "shell shock" at least as far back as WW1 which is also used in retrospectives/definitions of PTSD as a diagnosis, so this last clause doesnt ring quite true for me. i also think our understanding of PTSD could be improved, may require expansion/elaboration