Even fit and healthy people can have unremarked underlying conditions that pop up and surprise everyone. Plus there is a condition, whose name and details escape me, that can affect fit and healthy types, particularly athletes. A friend of mine, a lifelong runner and to all appearances super fit (apart from having destroyed his knees through running on hard surfaces) died suddenly at a wedding reception. His heart stopped, and he went down like he was poleaxed. Luckily that saved him, as hitting the floor restarted his heart. I think it was a similar condition that gave a Swedish (?) footballer a heart attack on the field during last year’s Euros soccer tournament.