Was he an older dog?
The reason I ask is that if he was a younger dog in good health, this is not something you'd expect. He may have ate something poisonous. Back when I was a kid in Hamilton, we had a nutbar neighbour who used to leave poison out in his yard for dogs and cats. I remember my father would freak on him, but the guy was just some complete psycho, so eventually the old man just took to going into his yard and taking the poison away.
Anyway, I was just wondering if the dog could have got into something?
If he was an older pooch who was on his last legs, then it's not a bad way to go. He was at home where he had a good life and people cared for him. We should all be so lucky.
That said, the death of a pet can be devastating as they usually are the best of the best things. I had to put my pet cat down last September (she had cancer of the jaw and she was 18 or 19 (not sure as she was a cast away kittie that no-one (but me) wanted))). She was just a little cat, but she meant a lot to me and brought me a lot of joy in life. I still get busted up when I think about her. Even though she had a good life with me, I'm still sad at her passing. If someone had of offered me a million bucks for her, I would not have sold her. (Seriously.) So I am sorry for your loss.