I rode him again the next day, and he still ever-so-slightly stiff. In truth, he might have been sound, but I tend to be hyper sensitive to every footfall when there has been an issue. I did add some trot work out in the field near the end of the ride, and he felt pretty good out there.
I don't let myself worry about this kind of stuff, especially when he gets visibly better each day. As a precaution, I did cancel my Monday lesson; no point in overdoing it. I'll work him lightly throughout the rest of the week so that by this weekend, he should be back to fighting trim.
Yah for expensive, if not proven, therapies!