Did you know that having a window seat during a long plane or bus ride is comparatively risky? No, it's not because you could get sunburn, but because you probably won't stand up and stretch your legs much.
"If, on the other hand, you have an aisle seat, you'll likely have to get up fairly often to let out someone sitting next to you. This movement helps prevent a blood clot," says Dr Tomas Jelinek, scientific director of the Düsseldorf-based Centre for Travel Medicine (CRM).
A blood clot (thrombus) can form in a blood vessel, for example a deep vein in the legs, when something keeps blood from flowing freely. The condition is known as thrombosis.
"Even young, healthy people and athletes can develop thrombosis," Jelinek says. Symptoms include pain and swelling in a leg.
"If you have thrombosis, you should actually remain lying down for several days until the blood clot has dissolved," he says. Otherwise it can be very dangerous.
A case in point: Following a long flight, a traveller stands up from their seat, ignores their aching legs, walks over to the baggage carousel - and drops dead.
"This happens because the muscle movement causes the blood clot to suddenly break free. It then travels through the heart into the lungs, and a pulmonary embolism [blockage of an artery in the lungs] occurs," explains Jelinek. "At worst, the result is sudden death."
The good news is that there are simple things you can do to prevent thrombosis. "It helps to drink plenty of fluids, for example water or tea, and to move around," says Jelinek.
In addition, he says travellers should wear compression stockings, also called support stockings: "They're advisable for anyone travelling for longer than four hours, and definitely for six hours or more.
"People at heightened risk - those with damaged blood vessels, a weak heart or who have already had thrombosis, for instance - should wear them on shorter trips too."
The stockings work by squeezing leg tissues beneath the skin. "This improves blood flow in the veins. You can imagine it as a river that's made narrower and therefore flows faster again," explains Jelinek.
Compression stockings come in various lengths and pressures. Jelinek says travellers who aren't at heightened risk of thrombosis can wear class 1 stockings: "They're comparatively comfortable, reach to the knee and are easy to put on."
Travellers at heightened risk would do better to wear class 2 stockings, which exert more pressure, he says, adding that before a trip they should consult their doctor about a prescription for a blood-thinning medication.
Aspirin, by the way, is ineffective at preventing deep vein thrombosis. "The drug is good at protecting against a heart attack. It works in the arterial branch of circulation but isn't effective at thinning blood in veins," Jelinek says.
Arteries carry blood from the heart, and veins carry it back.