Hello and welcome to pet lovers. Who did you speak to when you called the vet? I mean when you say "they" didn't seem concerned. Remember that the person who answers the phone is a receptionist, and while they do have an important job, giving medical advice on your pet is NOT one of them.
Get your boy back to the vet right away. I never heard of this happening with PU, but that doens't mean it can't.
And please let us know what you find out, and how your boy is doing. I hope you have him on a canned diet, now, forever?
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