Provided you have been given the go ahead by your doctor, there is no reason not to exercise. When doing so, though, avoid any sudden postural changes, particularly when your head is level with or below your heart. The lack of circulation could leave you dizzy and faint. Certain exercises like sit ups, bench presses, reverse flies and inverted yoga poses (think downward facing dog and forward bends) could all be risky exercises for you. As can aerobic exercise without a proper cool down. If practicing cardio, make sure you don’t move too quickly through intensities, rather lowering or raising them gradually. Keep your strength workouts vertical where possible, or make sure your head does not dip and peak above below and above your heart too rapidly. If your case is severe, ask your doctor if sodium tablets will help.