Air Canada flight AC878, a Boeing 767-333ER. experienced a 46-second pitch excursion while en route at night over the North Atlantic Ocean. This resulted in an altitude deviation of minus 400 feet to plus 400 feet from the assigned altitude of 35 000 feet above sea level. Fourteen passengers and 2 flight attendants were injured. The seatbelt sign had been selected ?on? approximately 40 minutes prior to the pitch excursion. The flight continued to destination whereupon 7 passengers were sent to hospital and were later released. Findings as to Causes and Contributing Factors 1. The interrupted sleep obtained by the first officer prior to the flight increased the likelihood that rest would be needed during the overnight eastbound flight. 2. The first officer slept for approximately 75 minutes which likely placed the first officer into slow-wave sleep and induced longer and more severe sleep inertia. 3. The first officer was experiencing a circadian low due to the time of day and fatigue due to interrupted sleep which increased the propensity for sleep and subsequently worsened the sleep inertia. 4. By identifying the oncoming aircraft, the captain engaged the first officer (FO) before the effects of sleep inertia had worn off. 5. Under the effects of sleep inertia, the first officer perceived the oncoming aircraft to be on a collision course and pushed forward on the control column. 6. The frequency of training and depth of the training material on fatigue risk management to which the flight crew were exposed were such that the risks associated with fatigue were not adequately understood and procedures for conducting controlled rest were not followed by the flight crew. 7. Although the seatbelt sign was on and an announcement about potential turbulence was made, several passengers were injured during the event because they were not wearing their seatbelt.