For anyone who's flown long hours in the back of a plane, the overcrowded experience is uncomfortably familiar.
It was worse for Val Clark, reports CBS News Correspondent Richard Roth. Five years ago she was cramped in economy class with her feet on her bags on a long flight from Minneapolis.
When she got home to England, she felt awful.
"I couldn't walk. The legs wouldn't take me I couldn't even feel my legs," said Clark.
Doctors found a blood clot. Her left leg had to be amputated below the knee. Val Clark is now suing the airline, claiming she's a victim of what's been dubbed "economy class syndrome."
"I go to bed at night and I pray that it's a bad dream," said Clark.
The medical condition is "deep vein thrombosis" -- a blood clot, usually in the leg, that forms when circulation's restricted, and can kill if it moves to the heart or lungs.
Air travel is by no means the only cause, but with cramped seating, lack of exercise, and dehydration that thickens the blood -- some researchers say it's a risk factor.
Farrol Kahn, of the Aviation Health Institute, says most people aren't aware of this risk from flying.
"This is one of the reasons why there hasn't been an uproar about it, because very few people make the link between the flight and their condition," said Kahn.
Now British surgeon John Scurr is trying to find out how strong the link may be, scanning travelers' leg veins before and after they fly.
"We see a large number of patients who in a few days of flying great distances present with a swollen leg; some present with chest problems, some may collapse and indeed there have been a number of deaths," said Scurr.
The aviation industry says the problem is rare and it's not directly a fault of flying. But some airlines now tell passengers it's a good idea to flex and stretch for better circulation, even when they're strapped in their seats.
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