Post-flight blood clots can catch even seasoned travelers by surprise, as travel writer Lindsey Campbell recently found out. She stretches before flights and moves around as much as she can—but after landing, she dismissed her calf pain as probably an injury from hiking.

Blood clots can form in veins deep inside the leg (hence the name “deep vein thrombosis” or DVT) if your knees are bent and you don’t move your legs for hours. The resulting clot forms in your calf, and causes soreness that proceeds to extreme pain. Here’s how Campbell describes it:
After a flight—or, really, anytime—it’s good to know the signs to watch out for. If the clot is in your leg, you may experience:

• Swelling in the lower leg
  
• Cramps or tenderness in the lower leg
  
• Redness or bruising
  
• A swollen area that is warm to the touch
  

Typically the symptoms are only in one leg, or more severe on one side than the other.
What’s worse, pieces of the clot can break off and travel to the lungs, where they can interfere with…