That's understandable, and I've never had a siezure in my life but I've had sleep paralysis, so I can get how losing control of your body like that would be very cumbersome to put it lightly... or well, as lightly as one can put it whilst using the word "cumbersome."

Although surprisingly enough you don't need a lot of focus for Stoicism. The real trick to it is to learn how to make your problems smaller. A siezure is a good example. A Stoic wouldn't fight the siezure or counter it, but rather focus on how it will pass, how everything will be okay and how life goes on.

Instead of increasing your discipline, Stoicism does the opposite, it makes your situation less demanding by only examining the immediate practical nature of what you're dealing with. And once you've done that, then you just relax.

Stoicism is about finding happiness by examining what you can do, and then doing it, and after you've done all that you can do, then why worry?