Passengers were unaware of the incident while the pilots snoozed.
The packed Airbus A330 was traveling to the UK last month when the two pilots made an agreement.
One sleeps while the other watches the plane.
The only problem with their plan turned out to be they both fell asleep at the same time.
The pilots had apparently only slept for five hours each over the last few nights.
One of them woke up and saw the other guy asleep, realizing the plane was unsupervised.
The Civil Aviation Authority says the incident happened on August 13 just after the plane carrying over 300 passengers reached altitude.
One of them woke up to find that they had both been asleep at the same time, and had no idea how long they’d been out.
The pilots voluntarily reported their incident to the CAA.
An airline spokesman said the two will likely not be disciplined.
The CAA has so far refused to say which airline the two worked for.