This was the front headline in today's London Metro newspaper.
Deep vein thrombosis has been associated with long plane journeys where passengers are immobile for long periods.
I didn't get to read the article, but it made me wonder if this going to be the new RSI (repetitive strain injury suposedly caused by too much keyboard work or repeated small movements).
If taking a long plane/train ride you need to drink a lot of fluids and get up and walk around at least once an hour. As Dave says very dangerous and not TMS. -Stryder