Swelling is often in the lower area of the body like legs and ankle during hanging position because of gravity. Other reasons why sweeling and red spots appear could be any peripheral disorder like DVT, sometimes when BP raises high you suffer from edema and itchiness because of which red spots appear.
So in such case let me recommend you to please take some precautions and if it appears again then immediately contact some doctor to rule out the exact reason by various investigation procedures:
1. Try to elevate your legs whenever you are lying down, to a position above your heart.
2. Immediately do some ice
massage over the area.
3. Perform some calf exercises so that blood circulation is maintained.
4. Wear stockings during your travel.
5. Wear loose fitting clothing.
6. Do not sit in one position for long. Try to change position frequently.
7. Avoid a position in which you have to hang your legs.
8. In office place small stoll under your foot while sitting and change the positions so that your leg does not comes directly in against gravity position as there are chances of increase in sweeling.
Please follow the above instructions/treatment. If still there is no relief then as an advice please visit some near by doctor for investigation as there may be chances of DVT or any thrombotic problem..
Good Luck and Get Well Soon