it is a really bad idea to not ride for a couple of weeks then to suddenly ride a lot of different horses for an hour or more each, especially one that is about 70% percheron and turns the rider into a human t-junction once on board
ooh I know what you mean, I hadn't ridden for years until I went on holiday and rode a 16'2" armchair (more like a sofa actually, with feet like upturned buckets) for an hour up and down steep twisty hillside tracks. He was a darling but I'm only 5'2" and very short-legged so it was agony for a few days after! The best thing you can do is make sure you get on a horse tomorrow, just for a little while. It will be painful at first but you will feel better afterwards. Btw, when I saw your title I thought you'd taken up kick-boxing or somesuch.