Treatment of these illnesses is symptomatic, meaning that one tries to make the symptoms better. Sometimes this is very successful, sometimes it is not. Some kids get better over time. Others stay the same or get worse. You have to do what you can and hope for the best.
Patience is a necessity.
These illnesses are stressful. They cause depression and anxiety. Deconditioning makes these illnesses worse. A program of mild exercise or slow activity that does not cause crashes can help a lot. For more on this see my page on helping orthostatic intolerance .