I recently took a trip too, and seemed to have a similar response with my feet/back to you. Here are my thoughts to ponder....
You had major back pain your second day there...I had back pain too after my flight...I suspect from sitting still on the plane for several hours (although I didn't 'white knuckle' it this time - I don't move much when flying). A trip to Ireland is a long time to be sitting still - and if you have any problems with your sciatic nerve...maybe that aggravated it?
When your back hurt - you're feet didn't. I think that someone here - some time ago described this as the 'Gate Theory'. Your brain can only register so much at once - and if it's preoccupied with the intense pain coming from your back, it 'forgets' about the pain in your feet. Some element of acupuncture works on this theory too - the needles provide a stimulus for the brain to focus on, sort of disctracting it from the pain (although this certainly isn't all that acupuncture involves - it does seem to be a little tiny piece).
Now that you are back - your feet are worse. I had the same thing happen. When I really focused on why that might be - I suspect that even though I did a lot of walking on my trip...I still spend more time on my feet at home. I spend a lot of time in the kitchen, and running up and down the stairs - doing laundry, driving etc - things I did not have to do while on vacation. I think you are also right about a stress connection though, stress can do all kinds of bad things to your body - so why not your feet too?
The connection with your back and feet? I had sore feet and a sore lower back on Thursday...had a 1 hour massage and my feet and my back both felt better. When my feet get worse, my back gets worse and vice versa. I don't have any answers - but I think that there are lots of us out there (out here?) that share your assortment of mysterious symptoms.