Clues to Why SkyWest Airlines Passengers Fainted in Flight

— -- Investigators have yet to announce what caused three SkyWest Airlines passengers to become ill and lose consciousness mid-flight, but some experts seem to agree on one thing: cabin pressure most likely played a role.

Dr. Michael Anderson, chief medical officer at the University Hospitals Case Medical Center in Cleveland, said people can respond differently to reduced oxygen and, even in a correctly pressurized plane, they might end up fainting.

"Although oxygen levels are normal ... a slight change in oxygen could cause a person to faint," he said.

SkyWest Airlines confirmed today that three people suffered a "loss of consciousness," but said there were "no indications of a pressurization problem or other issues with the aircraft." All three passengers recovered Wednesday after the plane made an emergency landing in Buffalo, New York.

Despite the company's statement, the Federal Aviation Administration said the pilot feared a potential cabin pressure problem and dropped the plane to get breathable air.

Anderson said when a passenger faints, the goal is to improve the person’s circulation either by giving oxygen or elevating the legs so the brain can get enough oxygen.

He said it’s also wise to check whether the person had underlying medical conditions such as diabetes. A worst-case scenario would be if a patient was in the middle of a cardiac arrest that would necessitate a defibrillator to try and save him or her.

But because multiple people became ill in this case, Anderson said there could have been a combination of things that lead to their losing consciousness.

"I think the word that comes to mind is multifactorial ... are multiple things adding to this situation?" he said. "Some people really stress out about flying [or they] haven’t eaten."

Anderson said in these circumstances there's also a possibility that "crowd mentality" played a role. Passengers who see a person pass out, if they are in a slightly less pressurized cabin, could end up having similar symptoms.

Mary Cunningham, a registered nurse and fellow passenger, assisted the sick patients on the plane and said she also started to feel sick after helping them get oxygen.

"She was gray, her color looked awful, as soon as she got the oxygen she was alert," Cunningham told reporters of the first passenger who fainted.

The pilot feared a potential cabin pressure problem and dropped the plane to get breathable air, according to the Federal Aviation Administration.

John Nance, ABC News’ aviation expert, said continued depressurization in a plane, even slightly, could result in passengers’ feeling ill or sick before cockpit alarms go off, whether alarm bells go off and overhead oxygen masks fall.

Also, with less oxygen, some passengers who exert themselves will feel the effects more strongly.

“The tell-tale thing is when the nurse gets up,” he said, “and gets to feel woozy.”