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Leg cramps (well not for you first-class darlings), crying over a movie you’ve seen 100 times or suddenly really enjoying that Bloody Mary, surely something is going on with our bodies when we’re 30,000 feet in the air.

Dr. Christopher Sanford, MD, MPH, DTM&H, an associate professor of family medicine and global health at the University of Washington, is here to answer a few questions.

What happens to our bodies when we fly?

Jets are pressurized not to sea level, but to the equivalent of 6,000-8,000 feet of elevation. Hence, the level of oxygen in our blood is reduced when we fly. Most of us, at rest, will not notice this difference, but some travelers with chronic medical conditions may feel short of breath when they fly.

Those with cardiac or pulmonary conditions, including coronary artery disease or chronic obstructive pulmonary disease (COPD), should consult with their physicians prior to travel, regarding the advisability of traveling with supplementary oxygen.

Reduced oxygen, decreased humidity, prolonged sitting and cramped quarters can result in fatigue, headache, a sore back and a generally grumpy attitude.

Super-long flights, e.g. Newark, New Jersey, to Singapore (eighteen and a half hours!) will only exacerbate these symptoms.

Related article: Why Bloody Marys taste better at 30,000 feet?

What are the best ways to alleviate the symptoms?

A good strategy by which to feel minimally frazzled when you fly is to treat the entire experience like an endurance athletic event – sleep when you can, drink a lot of water, avoid alcoholic beverages, wear comfortable clothes, stretch and walk regularly.

Do people actually cry more when they're on planes?

The short answer: yes. I've noticed it myself. I've teared up at schmaltzy movies. The reduced level of oxygen in the blood – exacerbated by engine noise and stress –may affect our emotions and decision-making.

Excerpts from Staying Healthy Abroad: A Global Traveler’s Guide

Is there anything I can do to avoid jet lag completely?

Sure. Instead of flying east or west, fly north or south. When you fly north or south there is no time change, hence no jet lag. Flights from Vancouver, British Columbia, to Baja California, or New York to Lima, or London to Ghana, all occur in a single time zone.

Is melatonin a good option to eliminate jet lag?

This is controversial. On one hand, I’ve heard a number of reports from people who feel it reduces jet lag symptoms. On the other hand, it’s a hormone that has a number of influences on your body, and – here’s why I come down on the ‘nay’ side – studies are lacking. No one has taken a large group of international travelers, given them a standard dose and monitored them for efficacy and side effects. I do not recommend this hormone. I do not think it has been proven effective, and I do not think it has been proven to be safe.

Given we’re talking about a condition that resolves after a few days without treatment, I’d vote for no drug at all. At some point, someone may do a randomized, placebo-controlled clinical trial and show that melatonin is great stuff. But as of now, the jury’s still out.

Additionally, in the US, melatonin tends to be sold at health food stores and is not regulated by the FDA; the result of this is that concentrations vary between different preparations, and, unlike drugs that the FDA regulates, potency may vary significantly between lots.

Some medical researchers distinguish between jet fatigue and jet lag. The former is characterized by general fatigue resolving after a single night’s sleep, and the latter is characterized by poor sleep lasting for several days (about two-thirds as many days as time zones crossed for eastward travel; about half as many days as time zones crossed for westward travel). Melatonin may reduce the symptoms of jet lag, but it isn’t known if this is due to melatonin’s effect as a soporific or as a hormone.

Children and pregnant women should avoid melatonin.

Related article: How a pulmonary embolism nearly canceled my honeymoon

Dr. Sanford is the author of Staying Healthy Abroad: A Global Traveler’s Guide.