Poor Merrick, seizures are frightening when you first see them and these poor babies don't understand what's happening to them. Because dogs talk with their bodies, I imagine it was scary for Zatara too. He's not used to seeing a dog flailing about and stiffening up, he just didn't understand the body language he was seeing in dog terms and it frightened him.
I had a Lhasa Apso with epilepsy. We never had to put him on meds because his seizures were rare. When they happened though, they were awful. There was that metallic smell, drooling and the stiffening of body parts, his eyes looked like they were ready to pop out of his head. We just held him when he had a seizure. Buster's seizures lasted only about 10 minutes and they were done, there were no lingering effects from the seizure.
I don't have any advice to offer you, I'm so sorry that poor Merrick has to go through this. When you have time, do some Googling about diet and epilepsy, there are some Vets that believe you can minimize the number of seizures with meds and diet, by eliminating grains, dairy and other foods. There *could* be some truth to it, (the diet theory) my daughter and I noticed Busters seizures seemed to happen after he consumed smoked meats or pork. Again, Buster had a very mild form of epilepsy.
Sendings good thoughts Merricks way.