We've had this happen several times with Rowdy - it happens sometimes when he travels with us, and sometimes when we leave him at home.
When his bowels get inflamed while we are gone on vacation and leave him home (which happened while we were gone to Alaska the past 3 weeks), the vet thinks it is the stress of us being gone - makes you real anxious to go on another vacation
It seems to only happen when we are gone or when he travels with us, so there has to be a correlation.
As mentioned, he will sometimes get it, but not as bad, when he travels with us. I have started giving him bottled water instead of tap water when we travel and the last trip to New Mexico for 2 1/2 weeks in May, he did not get diarrhea. I am hoping that this will do the trick from now on. Last summer on our trip to New Mexico, both he and Rexy got guiardia
The vet out there said it was from either drinking water from the river or from some animal poop they got into on a walk.
Now my hubby and I don't even drink the water when we travel - we only drink bottled water or soda and we find that it keeps our pipes functioning better while we travel.