Research has revealed that some people become more emotional when they watch a movie in the air than when they're on the ground because of the "intimate" nature of the inflight entertainment system.
Stephen Groening, a professor of cinema and media at the University of Washington, said: "The configuration of inflight entertainment apparatus produce an affect of intimacy that might lead to heightened emotional responses. Crying on airplanes actually consists of tears of relief, not tears of sadness."
And Stephen Legg, professor of ergonomics at Massey Univeristy in New Zealand, went as far to suggest that a person's mood can be altered by the cabin pressure they're experiencing whilst in the air.
He added: "We have shown that some aspects of mood can be altered by exposure to cabin pressures equivalent to altitudes of 6,000-8000ft.
"We know very little about the effect of exposure to multiple mild stressors on complex cognition and mood. But we do know that there is a general 'fatigue' associated with long distance air travel, so I guess it is probably the combined effects of these concurrent multiple mild exposures that give rise to 'flight fatigue.'"
It has also been revealed that "cognitive deficits become more noticeable" on older or less fit people whilst they are travelling.
Jochen Hinkelbein, president of the German Society of Aerospace Medicine and assistant medical director for emergency medicine at the University of Cologne, said: "There hasn't been much research done on this in the past as for healthy people these do not pose much of a problem. But as air travel has become cheaper and more popular, older and less fit people are travelling by air. This is leading to more interest in the field.
"A healthy person like a pilot or passenger should not have cognitive problems at this altitude. When you have unfit people, or someone with the flu or pre-existing problems, then hypoxia can decrease oxygen saturation further so cognitive deficits become noticeable."