[YorkOfTheShire]

Don't laugh at me please, I'm not a dog expert.

But...you know how if we (as humans) overexert ourselves whilst undergoing strenuous exercise, we can get a stitch in our sides and get upset stomachs including heaving, and the runs in worst case scenario)?

Is it possible that the run was simply too much for him to handle? It seems to me on a really hot day and that much running time for that length of ground...seems like an awful lot for a tiny dog (especially given the heat and frequent stops for water intake). Excess water intake during strenuous exercise in the heat is a really big factor in side stitches.

Like I said I'm not a dog expert - but I do know that when I overexert myself in the heat it really is not a pleasant result (dry heaves, limps because of stitch in the side and shin splints, etc) and diarrhea, so I've learned to take it easier the older I get.

Maybe it was a bit too much exercise?

When he was sick before was there a lot of exertion beforehand? Like a really long run, etc?

Forgive me if this isn't my place but I'm just thinking it (might) be possible (but I don't know).