A recent question Cat suddenly became paralyzed has a cat with sudden onset paralysis, after starting a new drug. The companies drug literature does not list this as a side effect, but the OP found that several pet owners had seen paralysis after administering the drug.
although I did find pet-owners who had the same experience on related forums.
You've done the research and there really isn't any reason to think there's a link between the felimazole and your cat's new symptoms.
I'm referring to the listed side-effects from studies.
What are the actual legal requirements for pet medications? Does the vet or the manufacture need to report this possible side effect?