Hi karen.
I used to feed and water a stray cat that had seizures. I took her to the vet and the vet recommended we leave the puss untreated, she reckoned that given the cat's age and the fact that she was feral, it would be kinder not to treat her rather than put her through the stress of treatment..
The vet reckoned it looked worse than it would have felt for the cat (it was horrible to watch, as you know).
Sorry, I know this is not advice - and your cat's not feral - just wanted you to know that the vet seemed to think it wouldn't feel as bad for the poor puss as it looked.