How do you cope with postural orthostatic tachycardia syndrome?

Phys therapy helps. This syndrome (aka "p.O.T.S.") can be extremely difficult to treat. You need to look for very specialized centers, with expertise in this disorder. You essentially need to "work out" your autonomic (involuntary) nervous system that controls heart rate and blood vessel tone. Physical therapy exercise can help retrain these nerves, often much more effectively than medications.
With difficulty. This is often difficult to treat successfully. First, you need a tilt table test to confirm the diagnosis. If confirmed, volume expansion by eating a high salt diet and drinking plenty of fluids may help. Beta blockers, Fludrocortisone (florinef) and midodrine (proamatine) are used with variable success. Good luck.