please talk to me

My cat went to an annual vet visit yesterday and they took a urine sample because he had a history of getting urine crystals. During the taking of the sample he had a seizure and could be recovered. Nobody knows what happened. He was healthy and young and he was my best friend for five or so years and I don't know what to do. I don't know how to deal with this. It was a completely normal checkup. My mother works as a tech there and it just... It shouldn't have happened. He should still be here