I think you will never know and as I lost my beloved Westie, Wilson, December 3 and still have a broken heart - my
sympathy is true empathy, I know h you feel.
In my case I know a tumor,, likely cancerous, ruptured my little Wilson's intestine, and whil we were in an animal hospital that could do the needed surgery, the dog had been in pain most of the day and even prescription intravenous pain killer wasn't making him comfortable.