[user104658]

Yeah to be classed as that at just 56 is odd, it's sometimes listed for very elderly people who will have multiple conditions so no single condition can be neatly listed, but at that age for it to be so sudden (no known underlying illness or condition) it would pretty much always be heart, seizure or aneurysm. Even "sudden adult death" is more accurately sudden heart failure, just without a known cause or pre-existing heart condition (basically it's likely that there is a cause, it's just not medically understood yet).