My father was in Vietnam and I had the exact same experience with him. Just out of the blue like it was playing in his head. Worst part is him and the friends he lost have never been acknowledged as having been in the conflict due to some shady government shit and an NDA. So not only has he had to live through that he has been accused of false honour for even mentioning it. But having met a few veterans of combat you can't fake that retelling, when you see them it's clearly real and running in their head.