My condolences as well, but with a word of caution. The symptoms you describe and sudden death are often seen in dogs that have ingested poison... usually an arsenic deriviative, which is the favorite of people who intentionally poison dogs.
I'd hope that your dog hadn't been out and about or some other facts that would rule out that possibility, but, over the years we've lost 2 dogs to intentional poisoning...
We've also had friends that have lost dogs to ingestion of antifreeze (Ethylene glycol) used in cars. I'm sure you vet would have recognized such symptoms, but sometimes the obvious is overlooked.
Again, sorry for the loss...