A pilot continued to fly after his co-pilot suffered a cardiac arrest and died – believing he was playing a joke.

‘The surviving pilot recalled how during the taxi the pair were talking normally and his colleague, who was also a flight instructor, had remarked “looks good, there is nothing behind you”.
His head then rolled back and the pilot, who knew the instructor well, thought he was pretending to take a nap, the report said.
As the plane turned the instructor slumped over with his head resting on the pilot’s shoulder.
The report said: “The pilot still thought the instructor was just joking with him and continued to fly the approach.”
He later “landed normally” before he “realised something was wrong” and made a call for help.’

https://www.bbc.com/news/uk-england-lancashire-64716821