Anyone start their dog with phenobarbital? Have some questions.

My 4 yo husky/German shepherd/American Eskimo/Shetland sheepdog breed recently got diagnosed with epilepsy. He had his first seizure on mothers day, second one 6 weeks after, 3rd one 3 weeks after. His neuro vet diagnosed epilepsy and prescribed phenobarbital. It’s his 3rd day so far and he looks like he’s drunk, no strength in his legs stumbling around. Wondering if this is side effect of phenobarbital and it’ll get better later once my dogs body get used to it.