I'm so sorry to hear this. The loss is great, and my heart is heavy for you.
We had a little guy named Chewy who did the same thing about 15 years ago. He had epilepsy. The people who gave him to us never told us this.
He could have been medicated if we would have known.
I'm sorry to read this also. I would have the same questions at ginger and wonder if there is any chance he got into some type of poison?
I am so sorry your dog died. It's always harder I think, when it's sudden, like that with no warning. You did not have time to prepare yourself.
I can't tell you for certain what he died of. The vet could do what is called a "Necropsy" (autopsy) on him to find out the cause, if you really need to know.
It sounds very much like he had a violent seizure of some kind. Did he have any history of seizures?..... or epilepsy perhaps?