You might try adding some plain pedialyte to his water bowl the lasix might be robbing him of electrolytes.
If you haven't done blood work to check his thyroid in a while you might want to do that to see if he is being over or under medicated.
You might want the vet to test him for Cushings disease too. You can read about that here
http://www.marvistavet.com/html/cushing_s_disease.html
If you want to read up on seizures and causes this site is the best one I've found
www.canine-epilepsy-guardian-angels.com
Hope this helps you!
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