t be coming from the phenobarbital. The usual side effects
in canines from phenobarbital
use are lethargy, polydipsia (increased thirst), polyuria (increased urination), polyphagia (increased appetite), anxiety and weight gain. From the symptoms I think your vet is probably right on the money with the diagnosis of a mass in the brain, but I doubt that the tremors signify pain because you said they are of short duration.