captain went tech with food poisoning very early in the flight
This happened to me as the second pilot, when I was very new on a medium corporate twin. He authorized me to fly on 2 hours to the destination, as it was the most suitable airport (much larger than our origin), and I would have the best support there if needed. Happily, he was better, and well enough to monitor my approach and landing. After a good sleep that night, he was much better the next day, and our passengers not caused to be alarmed at all.