Yes, I agree with everyone above. He needs to have his Bile Acids Tested. The amount of pups with Liver Disease (LS and MVD) is so unbelievable these days, that I am kinda shocked that this Vet is not pressing about it.
Please do not wait for another seizure. Honestly, if this were my pup I would be finding a Vet in the area that has a better handle on the small breeds and one who know more about Liver Shunts.
What food are you feeding him? What treats? Does he have any odd behaviors?
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I just went back and read your first post, IMO this has to do with his liver and I would be getting him into a Vet for a BAT ASAP