I am so sorry to read your post, I know you are beside yourself right now with grief and so many unanswered questions. Sounds like he may have aspirated fluid (even a little vomit sometime in the past day could have caused this). Likely his heart just shut down and maybe even had a small seizure due to not enough oxygen.
Sadly Bulldogs are very resilient to pain and suffering and many times you don't know anything is wrong until it's too late- even though he may have been very ill- if he liked to follow you everywhere he probably would regardless of how he was feeling. You can try to take some comfort in to knowing he went quickly and he did not suffer too much. I know it's not a lot to hold on to, but at least he wasn't alone when it happened. Know his memory will in time bring you happiness instead of sorrow, but it will take a long time to come to terms with. Hugs to you.
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