After effects of overeating?

Our Bailey got into the doggie cabinet while we were out last night. He managed to tear open a small biscuit box that was mostly empty already. But also tore a hole in a large 5 pound bag of biscuits. We're not sure how many he had. When we got home he was a little more lathargic than usual. He's normally pretty laid back, but he seemed to be laying down even more. He then seemed to have a restless night, panting and crying at times all night. This morning he pooped 2x as much as normal at the door. He didn't make it outside. He pooped another good sized soft greenish poop on an afternoon walk. He's still been more lathargic today going slowly down the steps. He lightly squeals when we press against lower chest area. His appetite is still good. I can't think of anything else he injested. We're wondering if this is just afteraffects of overeating. We're not sure if we should take him to the vet or just keep an eye on him for a few days. The off and on panting bothers me as well as his tender underside. Can anyone provide advice or their experience?