I've seen a lot of memes recently concerning Vietnam flashbacks as the punchline. Even as a kid I remember hearing a lot about "Charlie was everywhere" in shows and movies. What makes Vietnam more horrifying than some other wars, even recent wars? Were the horrors just so recent and also heavily documented?
This is more of a culture shift than a difference in experience.
While Vietnam was unique in many ways, soldiers in previous wars had similar traumatic experiences. The Marine wading through the rice paddies may have had a different rifle that his grandfather on Iwo Jima, but he faced similar extremes of climate and a crafty enemy dedicated to his destruction. The nightmares he woke up to in '79 where likely the same ones that terrorized his predecessor in 1950.
The difference was that by the end of Vietnam, there had been a culture shift that made acknowledging the trauma faced by soldiers acceptable to the general public. Some of this came from the military itself-shell shocked veterans of the trenches of WWI got medical discharges and treatment, although it was limited to the state of medicine at the time .
Experiences in WWII and Korea further showed the nation that war sucks for those who fight. By the time Vietnam came around, the foundation needed for the general public narrative to change had been laid. Combined with general unhappiness about the war (a vast oversimplification, but Vietnam was much less publicly popular than its modern predecessors) this narrative change about PTSD was primed for the public to accept.
This leads to a situation where the general pop culture acceptance of PTSD is strongly tied into the pop culture view of the Vietnam war. Broken soldiers returning from an unjustified war is a strong narrative, one that has taken root in the national memory of Vietnam and strongly influenced the portrayal of that war.
Even modern media tends to follow these conventions. Exceptions tend to speak to us as violations of the common narrative, and are thus unique.
Easy Company of Band of Brothers fame are the strong jawed heros we expect. Their counterparts, the Marines portrayed in The Pacific are damaged, dirty, and broken in ways that scream later wars, an intentional choice on the part of the director.
Less recently, the conflic of the first Rambo is driven by the unhappiness of a Korean vet (the sheriff) at how his war has been forgotten. The sheriffs brutalness towards John Rambo can be seen as an expression of anger in the face of changing social views that validate Rambo's trauma but not the sheriff's.
Sorry if that was rambling, midnight drunk answers may not be best for Ask Historians.