Another seizure

Henry seized again last night. Just a few minutes past midnight. This time the disorientaion was really bad afterwards, he couldnt get his back legs up to walk. I am not sure how long he seized before we woke up. It was heartbreakng to see him with back legs splayed out on the floor, panting and heaving very hard, with feces and urine all over him. He was a very unhappy dog. We got him a grain-free fish based kibble. I wonder if he is allergic to fish? Or was it just the diet change that triggered it? I wish I knew exactly what to do.

=(