@bmfoster
Thank you for your insights. I just find it infinitely ironic that I can pass a test without being able to carry out the test task for the designated length. I had been able to walk for six minutes two years before, with fatigue at the end only a fraction of what I felt at the beginning of the second test.
One year before, the sleep doctor sent me to a neurologist (general) who watched me walk for 6 feet or so and judged I do not have Parkinsons, and said if I have fatigue, I should go back to the sleep doctor. Neither doctor had an idea to send me to a movement disorder doc. After I 'passed' the six minute walk I asked my primary care to send me to a neurology workup, where the doctor luckily for me turned out to be a movement disorder doc, who said there was reason to give me a DAT scan, and here I am.

Now I know I had been manifesting PD symptoms for some 8 years, but none of the docs I saw over that time, for my complaints of stiffness and fatigue,
had any notion of what to do except do tests over and over in their respective specialties. Yes I have anger over this.