What causes cats to have seizures?

The other day while I was cleaning the catbox, I happened to look over at Tiffany laying in her cat bed, and saw that she was having a seizure! She has never had one before. She is diabetic and on insulin, and had been doing fine for so long. I don't understand what happened. I took her to the vet and she stayed overnite for testing and observation. She is now on antibiotics,(for some sort of infection that she has, but they couldn't identify it as of yet) insulin twice a day, and special vitamins to help regulate her blood cells. She has lost a lot of weight, too. I am going to bring her in after she is finished with the antibiotics, which is about 2 weeks. They will test her blood again and see how she is doing. She is so out of it, tired and disoriented. Poor baby! All of my other babies are fine! Boo is ornry as usual, Tigger is really chunking out, maybe he needs to work out, ha, ha! Miss Kitty had 6 kittens, 4 of whom I found good homes for. They are so cute! 3 long hairs, and 3 short coats. They are about 3 months old now. please pray for Tiffany, I am really worried about her. Thanks! Nano.

 

Poor Tiffany. I hope everything will be okay. Keep us posted. She will be in my prayers.