After 3.5 hour car ride very swollen legs and ankles. lasted 3 days. normal bp. other time swollen after walking &bus. very swollen after flight. why?

Swollen Ankles: In my experience, the most common cause of swollen ankles is "Venous Insufficiency." Due to gravity and incompetency of the venous system, blood will pool in the legs and ankles, particularly with dependency (when the legs are down). Usually, the legs are normal in the morning (after laying down all night), and the problem gets worse the longer you walk. See a foot and ankle specialist

See below: Swelling of feet and legs could be from insufficiency where valves in veins cannot overcome gravity and blood settles in legs and feet. Lymphedema can also cause fluid to accumulate there. Elevate feet/legs whenever possible. Elastic stockings and compression therapy may help. See your physician for evaluation to find cause and get treatment.