A pilot flying over the South China Sea was forced to declare himself unfit for duty, suffering with shortness of breath and impaired vision.
While piloting the Perth to Hong Kong service he became incapacitated by the condition.
Hong Kong's Air Accident Investigation Authority (AAIA) deemed the incident as "serious", in their report.
Cathay Pacific flight CX170 was carrying 270 passengers and 13 crew when the pilot reported difficulties.
According to Fox News, with an hour left of the flight, the pilot announced to his passengers that he had been taken unwell and his co-pilot would be taking over.