ok, so it's not a reaction to vax or flea/tick chemicals.
From the kennel cough, his immune system has been stressed. It does sound seizure like, and it could be from the things you listed.
Iam isn't the greatest, and personally I would never feed it. Can you offer some boiled lean chicken and rice? or a little cottage cheese and rice? He is tiny and needs some food in his system. Also the pedilite and pedisure would really be helpful.
I don't have any real answers for you...sorry, but I would def not leave him alone and get him into your regualr vet as soon as you can
