Absolutely, PTS is real! There is a natural letdown when you get home. You've been on the road for days, weeks, or months. Every day on the road is a new adventure, filled with unknowns, new things to see, new people to meet, new challenges to overcome. Life feels very, very full. To come back suddenly from this to the "routine" cannot be expected to produce anything but a PTS reaction.
I do find that I need to be sensitive on my return when talking to people about the trip, to not overdo it. One thing that has helped is the fact that I journal my experiences daily during my rides, and so the people on my distribution list have generally followed the trip, some fairly intently. When I return, rather than having to start from scratch in describing the trip, I am able to engage those who want to talk about it at a more substantial level. That helps me with my transition back to real life, and I think those who are interested find it a rewarding conversation too.
But none of this prevents those occasional daydreams, when a particular memory from the trip just overtakes you. Best you can do at those times is just sit back, remember, and enjoy!