(CNN) -- It's happened to most of us. We suddenly wake up and find ourselves disoriented, wondering where we are, and possibly mistaking a light in the distance for something completely different. Usually it's no big deal -- you shake it off, wake up and move on.
If you happen to be pilot on a trans-Atlantic flight, the consequences can be much more serious -- like mistaking the planet Venus for another plane and sending the plane you're piloting into a dive that slammed passengers into the ceiling and back to the floor.
A report released Monday by Canada's Transportation Safety Board describes what happened on January 14, 2011.
The first officer on Air Canada flight 878 from Toronto to Zurich, Switzerland, was tired and needed a nap. The "controlled rest" is legal and an accepted procedure in order to improve on-the-job performance and alertness. With the captain's permission, the first officer drifted off for a few Zs.
While the nap is supposed to last no more than 40 minutes, the first officer slept for 75 minutes and woke up feeling unwell, the report states.
By that time, the captain had turned on the seat belt sign for some expected turbulence. There was also a U.S. Air Force C-17 nearing the Air Canada 767.
The first officer saw a bright object ahead of the plane -- the planet Venus -- and mistook it for the approaching C-17. The captain corrected him and said the C-17 was straight ahead and 1,000 feet below.
At that point, the captain of the Air Canada jet and the C-17 pilots flashed their planes' landing lights at each other to acknowledge their position.
But the first officer, still believing that the object in the sky above him was the cargo plane, initiated a dive to avoid the perceived imminent collision -- sending the jetliner toward the Air Force plane.
The captain saw what was happening and immediately pulled back on the control column in a frantic attempt to increase altitude. As quickly as that, the C-17 passed underneath the Air Canada jumbo jet with 103 people on board.
Within seconds, the plane had gone from its assigned altitude of 35,000 feet down to 34,600 feet and back up to 35,400 feet before finally recovering back to its 35,000 feet cruising altitude.
It sent passengers who were not wearing their seat belts flying.
"I was sleeping and I was literally and violently thrown out of my seat and was slammed into the ceiling," passenger Louisa Pickering told the CBC. "I hit the top of the ceiling and fell back to the ground."
Many of the passengers thought the plane had hit something.
"It didn't feel like turbulence," she said. "It was very sudden -- it felt like it was one violent bump."
The sudden drop was a shock for unsuspecting passengers.
"Some people were working on their laptops and had their seatbelts on," passenger Ashlyn O'Mara said in a CBC interview. "Their laptops went flying, completely gone, glasses went missing."
"People were screaming," she added.
Fourteen passengers and two flight attendants were injured.
"I do remember them asking for a doctor -- if there was a doctor," Pickering said. "There was a pregnant woman on the flight and she had some injuries."
The flight continued to Zurich, where the injured passengers and crew were treated.
The report says the incident points out a couple of inherent risks.
First, "North American-based pilots flying eastbound at night towards Europe are at increased risk of fatigue-related performance" issues.
It also gives credence to the warning you often hear -- but might ignore -- that passengers should wear their safety belts at all times when seated.