According to a 2011 survey by Virgin Atlantic, 55% of flyers become more emotional on flights. This may be due to the psychological effects of dehydration.
When a plane's cabin pressure is maintained at 6,000 to 8,000 feet above sea level, it can cause dehydration. As a result, the eyes well up with tears.
Brown continued, "You have to be emotional to cry, [so] your body acclimates to the dryness and creates the tears, but has to create the emotion first to create the tears."
Cabin pressure also causes oxygen deficiency. As Dr. Robert L. Quigley told CNN, "One person might feel weepy, another sleepy — hypoxia affects people in different ways."