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.
The incident which happened in February is still being investigated by AAIA.
A "PAN PAN" call was made to Hong Kong air traffic control, indicating an "urgent, but not life threatening" situation had occurred on the flight.
Passengers were alerted to the desperate situation when a call was made for any doctors on board to make themselves known to cabin crew.
This initial AAIA report shows that a "recognised medical professional" was found amongst the passengers, who was able to assist the suffering pilot.
The volunteer medic was able to relay the pilot's condition to a company doctor over the aircraft radio, while the co-pilot took control of the flight.
The report concludes that the flight landed, without further incident, at around 7am at Hong Kong International airport.
This is just the second incident this year under investigation by the AAIA, in which a Cathay Pacific pilot has been incapacitated due to "physical discomfort."
On January 26, the co-pilot of a Cathay Pacific Boeing 777-367 from Japan had to take over flying of the service to Hong Kong.