Passengers aboard an Air Canada flight helped restrain a pilot who experienced a medical emergency that they say appeared to be a seizure for about 40 minutes after the aircraft suddenly swerved midflight, according to a passenger who spoke exclusively with ABC News.

Air Canada said Flight AC7664, operated by regional partner PAL Airlines, was en route from Newark, New Jersey, to Halifax, Nova Scotia, on Wednesday when the captain experienced the medical emergency, the airline said.

The first officer took control of the aircraft and diverted the flight to Boston, where it landed safely. The captain was taken to a hospital for medical treatment, according to the airline.

The De Havilland Q400 was carrying 61 passengers. Air Canada said it is working to arrange alternate travel for those on board.

Rodney McDonald, who was traveling with his wife and two sons, told ABC News the ordeal began when the aircraft unexpectedly lurched.

“The moment the plane swerved, I knew something was wrong because it was not turbulence,” he said. “It really felt like someone had jilted the controls and then it happened over and over again. And, you know, every thought goes through your mind, you start praying. My boys instantly started praying.”

McDonald said a flight attendant rushed into the cockpit before pulling one of the pilots into the aisle.

“One of the flight attendants entered the cockpit frantically and a few moments later, he was dragging one of the pilots out of the cockpit onto the aisle way of the airplane,” he said.

McDonald said the pilot appeared to be experiencing a seizure, and he and about four other passengers helped restrain him while the co-pilot flew the aircraft to Boston.

Those potentially experiencing a seizure should never be held down due to the risk of further injury, the CDC notes. Instead, the area should be cleared of sharp or dangerous objects; they should be turned gently on their side, and their airway should be kept clear. 

“Yeah, it was really horrifying. I was sitting in the front row, my family was from their back, just the way the seat arrangement worked out,” he explained. “And I went back to sit with them and then realized that the pilot was out of control physically, not violently, like it was clear that he was not in control of his faculties and needed to be restrained.”

He continued, “[We] worked to get him under control, it was a fairly strenuous 40 minutes of keeping him down and using as many seatbelts as we could to restrain his legs arms and chest.”

McDonald said a registered nurse on board helped direct passengers and assist the pilot during the medical emergency, while he praised the flight attendants for remaining calm throughout the ordeal.

“The flight attendants were stupendous. They stayed calm,” he said.

Emergency responders met the aircraft after it landed in Boston. McDonald said he was grateful everyone made it off safely.

“We’re just grateful, grateful for how it all ended,” he added.