I wish I had seen this sooner. Has your vet taken an x-ray of your cat? My kitty has been showing the exact same "seizure" symptoms- not full on seizures but the stiffening, drooling, dehydrated and having trouble walking..... after 2 emergency vet visits, an IV catheter and a lot of valium, my vet finally took some x-rays and found that her colon was completely blocked and she had a ton of gas backed up behind it in the small intestine. They gave her an enema and she's SO much better now! Still having a little trouble walking but I think she's just sore from the IV (they had trouble getting it in and her back legs are bruised..), enema and rectal exams they put her through. Since she finally voided her bowels, i haven't seen any of those "seizures". I think she was just straining so hard to poop that what looked like a seizure was just her way of sayng "OW! I can't poop and it hurts!"
Hope your kitty ended up ok....
