I do not think there is a common way of passing for them. When my boy passed he was 7 yrs old and had one very bad day, his heart slowly gave out through out the day, he was sick in the AM and past that evening. Others have posted saying they found them passed when they got home, while others passed due to surgical complications.
it is not uncommon for a bullies her age to sleep 18 to 20 hours a day.
i tagged a few few members I know have experience with a loss of a bulldog