Serena Williams, 29, seems like the healthiest woman on the planet (have you seen the muscles on that body?). But sadly, in this case, looks can be deceiving. The tennis star recently suffered a pulmonary embolism, a blood clot in the lungs, during or shortly after a flight from NYC to LA and following a recent foot surgery. Usually, a pulmonary embolism is the result of a blood clot forming in the leg, breaking free, and traveling to the lungs. If untreated, the condition can be deadly.

And to make matters worse, Serena later had to undergo emergency treatment for a hematoma, bleeding beneath the skin, which likely resulted from treating her pulmonary embolism. Our expert, Los Angeles internist Dr. Andrea Ruman, explains that Serena "may have developed a hematoma due to any procedure where a needle entered a vein or artery, like during a routine blood draw. Or the hematoma could have developed spontaneously due to her blood thinners (or anticoagulation) treatment of her pulmonary embolism."

Serena is now home and doing better, with doctors monitoring her condition. But if something like that can happen to someone in that good of shape, we sorta start to question what could happen to chocolate-bingeing desk job workers like us.

According to Dr. Ruman, risk factors for pulmonary embolism include: "Travel of four hours or more in the past month (i.e., prolonged sitting or immobilization during a flight or car ride), surgery within the last three months, malignancy (especially lung cancer), history of thrombophlebitis (inflammation of the superficial leg veins) and trauma to the lower extremities and pelvis during the past three months. Other risk factors include a genetic predisposition to blood clots, birth control pill use, and pregnancy."

Dr. Ruman continues, "In Serena Williams' case the development of a pulmonary embolism was probably related to prolonged immobilization of her leg following recent foot surgery. In addition, she had recently been on a long fight from NY to LA."

So what can you do to try to avoid Serena's fate? "The best way to prevent a pulmonary embolism is to avoid its risk factors, as much as possible. So, for example, stop at least every two hours on a car trip and stretch your legs and walk. On long airplane flights, get up and walk the aisle at least once an hour to prevent blood clot formation. If you are predisposed to clotting, anticoagulants, such as heparin and warfarin, should generally be administered before and after an operation. And if you've had surgery, moving as soon as possible can help prevent pulmonary embolism and hasten recovery overall."