I have an 8yo who was JUST diagnosed with SPD through an OT, as the developmental pediatrician route is something like a 10 month wait... I'm still waiting on the paperwork and our pediatrician said to go to the OT b/c that is where they would send her for therapy anyway.
Traveling is extremely stressful for her (even when she is excited about the trip) unless she has been there before. Then things are a little easier. I took her to NYC in January and the meltdown that occurred was beyond belief. Her poor body was completely over stimulated and between the smells, the noise and going from dark lights to bright lights, she could barely stand to stay there at the peak of her confusion.
I was alone with her and it took all of my strength to keep my patience and hold on to let her chill out and get herself back in sync (words I know now but didn't know then). She eventually felt better and hugging a stuffed animal as we journeyed through the and had a fantastic time. But all of those changes are too much for her. She usually wants to eat only food she's eaten before - it is comfort food so, sadly we were at McDonald's a lot (which we rarely ever eat at home but it mad her feel better there).
If your child would happen to have SPD, it would make sense that he felt better mid-trip... he may have had the time to process the stuff, know how to handle it and know when to reach out to you when he needs help.
For our daughter the food stuff comes from sensory.
We have since found that she pretty much rocks the SPD (as in she has most senses being over responsive, it affects her posture, handwriting, coordination, smell, listening - well, you name it). She is so bright that she covers most of this stuff up very well where it is hard to believe she would have difficulty with anything developmentally. I am getting better at seeing when that fight or flight sensation is about to kick in and since she is so verbal, it makes it easier for her to say "that noise is bothering my super senses." She LOVES that she basically has super hearing and she jokes about it.
Right now we are trying to tackle the dentist, which is about to drive me to therapy myself. I thought we had a dentist who "understood SPD" but after the last appointment I'm not so sure.
If it is sensory, the one thing I've noticed with my daughter is that I can't really rely on anything. Some days things that bother her are the same things she didn't notice two days ago but when I think back, maybe the day before we were out a lot and I know she's super tired or she is getting sick. Goodness... anytime she is sick, there is almost always a HUGE meltdown the day before.
I also don't know what I would do without this place. I know I get a huge amount of peace from seeing anytime Grinity posts b/c she is always a source of kindness and encouragement. Best of luck to you! Keep us posted.
Homeschooling DD in PA