It doesn't matter if you're fit or unfit, male or female, wedged in cattle-class or sitting in the pointy end of a plane. We need to talk about deep vein thrombosis (DVT).
You've probably heard of it. You might've glanced at something about it on the back of an aeroplane safety card, or seen the circulation-boosting socks for sale in the airport.
Basically, DVT occurs when a blood clot forms in the leg. If it's big enough it can travel through the bloodstream and block the main artery to the lungs. That's very, very bad.
It usually occurs when you're sitting still for long periods, such as on long-haul flights, which it why it gets nicknamed "economy-class syndrome".
IF LEFT UNTREATED, IT CAN BE DEADLY
This week, a British coroner determined that a 51-year-old pilot died from DVT due to a delay in his hospital treatment.
Captain James Bedforth experienced shortness of breath when he flew from England to China in June last year, and he collapsed shortly after flying home the next day.
He'd gone to hospital two months earlier with a pain in his leg, but doctors failed to pick up the clots. When he was eventually treated with blood-thinning drugs, he was given too much.
He tragically died of a brain haemorrhage.
The inquiry found he was not told that shortness of breath could mean his life was in danger.
"Clearly Captain Bedforth was a very intelligent man who found himself in China in the midst of a long-haul flight," the coroner said. "I'm sure he was the type of person that had he been told about the shortness of breath issue, he would have acted upon this immediately."
Anaesthetist Ye Myint, who served as an expert, said the pilot should have been treated immediately, telling the inquiry "the delay may have changed the outcome".
The lack of awareness of the symptoms is, quite frankly, terrifying.
"I consider it unlikely that a senior pilot of Captain Bedforth's experience would have placed himself on duty on the flight deck of an aircraft if he had considered himself likely to collapse or thought himself potentially seriously ill," the coroner said in his conclusion.
SO WHAT ARE THE KEY WARNING SIGNS?
According to the Victorian government's Better Health website, you should look out for pain and tenderness in the leg; swelling of the lower leg, ankle and foot; and skin that is red and warm.
If you experience those symptoms shortly after flying, tell your doctor so they can look for clots.
You can also actively reduce the risk of developing DVT.
Avoid cigarettes and alcohol, drink plenty of fluid, and don't sit with your legs crossed.
Get up to walk around the cabin every time you finish a movie. Buy yourself a pair of anti-DVT socks.
If you're in a high-risk category, such as being overweight, a smoker, or having a history of heart disease, talk to your doctor.
Friends say Captain Bedforth was a "consummate professional" and a "larger than life" character who will be "sorely missed" on a fundraising page set up in his honour.
He's the devastating example that shows even frequent flyers who lead active and healthy lifestyles aren't safe from this silent killer.