Anyone note a disabling level of sedation from Keppra? Is this very uncommon?

Has anyone's dog been so sedated from Keppra 250mg that they can barely stand/walk, or eat, or drink? 

My 14 & 1/2 year old dog had a grand mal seizure out of the blue in February. A brain tumor was suspected. There were some possible neurological "episodes" or behaviors in the next few days. Ultimately my vet started her on Keppra 250mg Q8 hours. (She weighed 23 pounds.) From the first dose, it sedated her to the point that I could never have given her three doses in 24 hours. 

I've read that many of the anticonvulsant meds can make dogs wobbly and weak on their legs, but my dog could only stand with significant support. And I could sometimes get her to take kibble slowly from my hand, but she couldn't manage it easily, and she could scarcely lap up any water.

I begged for another med to be tried, but three different vets (my regular vet and 2 ER vets) felt that Keppra was the safest anti-seizure drug for a dog her age, who might possibly have a brain tumor. They seemed puzzled that she was so sedated, and said she would adjust over time.

I'm blaming myself, I feel like I didn't advocate for her well enough, though I tried to get my point across. Is it *that* unusual for a dog to have such bad sedation from Keppra?