Very nice chap called Roger, F27 Captain, '50s, fairly fit but not a fanatic,flew 2 rotations from Abu Dhabi to Das and back one morning in the 1970s, went off duty, no hassle, no problems, retired for his customary zizz and never woke up. Heart attack. Medical was all clear, ecg included, not all that long before.
If I were an F/O, which Praise the Lord I'm not, I would run through the "Capt Incapacitated" drill before every take-off with a 40+ Captain, but very quietly to myself.
You wouldn't want to demoralise the old git, now would you?