In the last week, he's developed a bump on his forehead that has gotten rather large over the week. Most likely lymphoma or another type of cancer either in his sinus cavity or in his brain. Probably what is causing his seizures.

Talking to the vet about palliative care for the next week or two.

I'll post as many photos of him as I can on my instagram in the coming days. If you wanna see them, https://www.instagram.com/chinotenshi/