Is the occurrence of deep vein thrombosis after long periods of inactivity such as a long plane trip, where lack of movement and low atmospheric pressure cause this ailment. In severe cases, the person may suffer a pulmonary embolism, if the trip is longer than four hours.

People with circulatory problems, and/or pregnant with varicose veins are prone to this ailment. Therefore, it is advisable to prevent it, by making feet and ankle exercises for the duration of the trip, drinking plenty of water to avoid dehydration, wearing comfortable clothes and not crossing the legs.