A study reported by the BBC discusses the many which in which travel by airplane can affect our consciousness and perception:

“Anxiety levels can increase with hypoxia,” explains Valerie Martindale, president of the Aerospace Medical Association at King’s College London. Anxiety is not the only aspect of mood that can be affected by flying. A number of studies has shown spending time at altitude can increase negative emotions like tension, make people less friendly, decrease their energy levels and affect their ability to deal with stress.

“We have shown that some aspects of mood can be altered by exposure to cabin pressures equivalent to altitudes of 6,000-8000ft,” says Stephen Legg, professor of ergonomics at Massey Univeristy in New Zealand, who is studying the impact of mild hypoxia on people. This may go some way towards explaining why passengers often find themselves crying at films more mid-flight, but most effects in scientific studies seem to only occur at altitudes above those that commercial airline cabins are set to. Recently Legg also showed the mild dehydration that might be expected on a flight can also influence mood.