The most important thing you can do for your eldery cat is keep him fed and hydrated.
You can have the vet give him subcutanious fluids to get him stable.That will keep fluid in his system for about 30 hours.
Next, get some unflavored pedialyte and when the fluids wear off, give him one dropper every 15 minutes for an hour.
Boil unseasoned skinlesss chicken breast til soft and blend to baby food cosistancy. You can use the broth for hydration as well.
If he won't eat you have to blend it to a gruel and feed it with a dropper. Give him two droppers every twenty minutes for two hours.
Your cat is feeling so poorly that he has given up. At this point he needs a jump start to get his systems going again.
Once he is fed and hydrated he will feel better and may be motivated to eat again.
Best of luck with him - please let me know how he is doing.
BTW: I recently went through this with my own 16 year old cat.He did not have seizures but would not eat because of other issues.

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Dedicated to Cats and the people who love them!
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