I wish everyone with PD and their families could read your letter. I think you express what most all PD people struggle with. I was diagnosed only 5 years ago and I have finally come to the same conclusion. You try every day to maintain and figure out what I can do or take to keep it at bay and at the end of the day I have no answer. There are just too many inconsistentcies within you and the environment each day to ever get an solid answer. So the answer is? " no one knows". Put one foot in front of the other, keep moving, exercising, taking your meds and smile even if you don't feel like it.