Most frequent travelers are aware of the risk of deep vein thrombosis (DVT) that comes with long flights (even flights of just four hours or more).

DVT, per the Mayo Clinic, “occurs when a blood clot (thrombus) forms in one or more of the deep veins in your body, usually in your legs” and “can be very serious because blood clots in your veins can break loose, travel through your bloodstream and lodge in your lungs, blocking blood flow (pulmonary embolism).”

A long flight makes you vulnerable to DVT because it leaves you stationary for an extended period of time, often in a cramped seat. This of course is bad for blood flow and why when flying you should try to get up from your seat about once an hour. In a revealing story for the The Points Guy, Lindsey Campbell—a healthy and oft-traveling 29-year-old—details her experience with DVT following a recent flight home from Iceland. She shares her symptoms and tips on how to avoid it. It’s worth reading before your next long flight. And because DVT should be taken seriously, here are a few more resources on the subject: