Unlike just 25 years ago, it's now hard to find someone who hasn't been on a plane.
It's a unique travel experience that human beings didn't do in significant numbers until quite recently. So it's no wonder it does some strange and unexpected things to us, including bringing us to tears.
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The reporting is anecdotal, but there's plenty of it: Virgin Atlantic even did a survey in 2011 that found "over half of respondents (55%) agreed their emotions become heightened when on a flight and 41% of men surveyed said they hid under blankets to hide their tears."
When we fly, we are more likely to cry -- but why?
The first reason is simple: We bring ourselves with us. That includes the myriad mental-health issues we carry.
"At every age level, across genders, religions, races and backgrounds, many people have one of the baseline mental illnesses, from claustrophobia to agoraphobia, and other various manifestations of anxiety -- they're ubiquitous," says Dr. Robert L. Quigley, senior vice president and regional medical director of International SOS & MedAire.
"The stresses of travel are enough to trigger anyone who has a baseline mental health challenge," he says.
Few would argue that flying isn't stressful: Getting to the airport in time, the intense scrutiny of security, then boarding the plane and ensuring you squeeze all your belongings and your body into small spaces -- as quickly as possible -- is a challenge.
If you're traveling solo, you're locked inside a small space with a group of strangers for the duration of your flight. These circumstances put many on edge.
And then there's the reason for your travel. Did you just say goodbye to a loved one or are you flying to a job interview or a place you have never been to? All of these things are stressful for even the most even-keeled people. Add in even a mild anxiety problem (anxiety is the most common mental illness, affecting almost 20% of the population) and it doesn't seem so curious why people might find themselves in tears once aloft.
Planes are also particular -- and often, particularly uncomfortable -- environments.
The ever-smaller seats and minimized legroom doesn't just lead to painful hips and knees.
"The smaller seating arrangement increases anxiety -- your basic physical boundaries are encroached," says Dr. Jodi De Luca, a Colorado-based licensed clinical psychologist and expert on altitude and emotions.
"It's not comforting to fly anymore. Our basic needs -- food and drink, blankets and pillows, aren't provided for. You're even limited to how much you can bring on-board to comfort yourself," she adds.
And then there's the cabin pressure, usually maintained at a level of 5,000-8,000 feet, which can have very real physical effects, depending on the person.
"There's a plethora of evidence that you go into a relative state of hypoxia [oxygen deficiency] when you're in flight," said Quigley.
The affects, she says, may not be realized by passengers.
"One person might feel weepy, another sleepy -- hypoxia affects people in different ways. There may even be hormones triggered by hypoxia -- it's all idiosyncratic."
Add these inputs together and it not surprising we cry at 36,000 feet. We feel physically weird, we have little control over our circumstances, and we may feel vulnerable.
Feeling this way, we might turn to in-flight movies, but anyone who has cried over a terrible rom-com -- yes, that was me sniffling along to "How to Lose a Guy in 10 Days" -- knows that sometimes media can work against reducing emotional feelings.
"There's something special about crying on board an airplane," says Stephen Groening, Professor of Cinema and Media at the University of Washington in Seattle, who has studied how inflight entertainment might have unique effects on travelers.
In a study on the subject, Crying while Flying: The Intimacy of Inflight Entertainment, he posits that "the technological apparatus of inflight entertainment generates a culture of intimacy [by creating] a relationship of extreme proximity between passenger and media form."
Groening thinks it might be the combination of stressors and the closeness of the media that conspire to bring us to tears.
What goes better with a film than a glass of wine? Alcohol may help reduce the anxiety of flying for some people, but it can also have a host of negative effects: It can exacerbate dehydration, which is already affecting most travelers due to the cabin pressure.
The physical and psychological effects of drinking plus cabin pressure are additive, says Quigley. So if you quaff a cocktail while flying, the two can exacerbate each other.
"Alcohol can make you more emotional -- so can hypoxia," says Quigley.
DeLuca doesn't advise drinking while flying and points out that it's dangerous to combine medication for anxiety with alcohol.
"You can go into respiratory failure," she says.
So what can you do if you feel emotional when you fly? One option is just to cry it out, as long as you can do so without upsetting other passengers. Everyone cries differently, it may be that you can shed tears in a private way.
But keep in mind that you are in public, says De Luca. She advises travelers to consider their own well-being as well as the others around them. So if you feel tears coming on, consider finding a private place to cry (which she admits is a challenge on most planes).
To avoid the tears, "If you are traveling with someone, talk your feelings out," De Luca advises as a first line of defense. If you are solo, she suggests distracting yourself, "So the brain is forced to think instead of feel -- do a crossword or Soduku, play a video game or play mental games using the alphabet."
Some find meditation podcasts -- Insight Timer and Tara Brach offer dozens for free -- helpful for calming and relaxing a racing or emotional mind.
Self-regulate what you are watching or listening to, and avoid media that would normally make you feel emotional, De Luca suggests.
That's easier than ever -- and may even change how often crying while flying happens.
"The thing that has changed about inflight entertainment is that people are bringing their own devices on board more often now. So we may see a decline in crying on board because people are choosing what to bring on a plane," rather than selecting from pre-chosen options, says Groening.
Some are skeptical that people cry more at altitude.
Dr. Paul Wicks published a study that showed people cried at the same rate they did at home, and called the whole concept we cry more while flying a "pseudo-phenomena."
Memory might be a play here too. We might also be that we remember the times we've cried on a plane better than other occasions we've shed tears.
"Crying by yourself isn't memorable to you the way crying on a plane is," said Groening.
Either way, it couldn't hurt to pack extra tissues.