When should you panic if your dog has diarrhea?

My 9-month old 15lb mutt started having loose stools yesterday evening, which progressed into liquid/pudding textured poops during the night (on the carpet….) I’m not sure what he could have eaten to upset his stomach so badly but maybe he got into something. I know he ate some onions, tomatoes, and black olives that were left over from a pizza. As far as I know he hasn’t touched his dry food since at least 8pm last night.

However he seems completely fine other than the diarrhea of course. He is still running, playing, barking, etc. No whining, listlessness, or any change in behavior at all.

I put him in the bathroom with a couple toys, water, rice, and a towel to sleep on… I just went in there to check on him, feeling sorry for him, and all he was concerned with was guarding his bone and toys… I think he likes being in his little cave?

Anyway, I know dogs get diarrhea sometimes, but when should I start panicking and take him to a vet? He just had a fresh bout of pudding poop about 40 minutes ago.

Oh I should mention we have another dog who is absolutely fine so far. Also they both caught worms maybe a month or two ago and we gave them deworming meds. They’ve both had their shots.