Hank has a tummy ache

So we had this great little storm blow through, the temps dropped about 20 degrees. 1/4" of rain, and I told Bill we should go for a late afternoon ride, so I go catch the horses and I tie Hank to the trailer, and he looks kind of dull eyed. I hang a little bucket with some feed in it and he refuses to eat it. VERY odd for this horse who lives to eat. I start watching him and looks uncomfortable. Starts watching his belly a bit. I check all the metabolics, and he is OK, nothing way off. Pulse 40, very slight dehydration, and while slight on his left side, he does have some gut sounds. I take him for a walk in the pasture, and he drops down, does a tiny roll, and just wants to stretch out. I let him, and watch him. Nothing really huge, just lays there quiet. I get him up, gave him a dose of oral Banamine, and watch him a bit. He passed some manure right before I gave him the Banamine. After about 30-45 min., he wants to eat grass and looks fine. Meanwhile I had called the vet who is over an hour away, and talked to him. He suggested I keep him away from food tonight, and just watch him, see if it flairs back up after the Banamine might wear off. Since it is easiest to watch him from the horse by having him tied to the trailer, I do just that. He was squirmy until he finally went pee and is irritated to be tied to the trailer. At this point I am guessing it was just the storm that gave him some digestive upset, but I thinking I should get him scoped for Ulcers. This is sort of what he had done at some rides in 2006. Not a huge colic, but just not comfortable, and then is better. Of course, this makes me worry about doing distance with him, and I question if he is just maybe not as suited as I thought.