One of the theories in finding ways to midigate POTS symptoms is to help reduce blood pooling in the lower extremities by strengthening the calf muscles.
A couple of months ago I started running with a tire. I'm now averaging 20-25 miles or about 1/4-1/3 of my total weekly training miles pulling a tire up and down a hill. I have noticed in the past month a significant decrease in my POTS symptoms overall, and a great increase in my energy level since I started pulling a tire.
I don't know if tire pulling will work for all people with POTS, but it seems that there might be something to this idea of strengthening the calf muscles, and even individuals who find running difficult may benefit from resistance or weight bearing exercises that strengthen calf muscles.
Marshall Ulrich has a good post about how to make a tire. I didn't make mine as fancy as his. I took an old camel back shell, stole a long piece of webbing from my husbands climbing bag (yeah it was his good one), and then he drilled a hole in my tire and basically just a bolt with a washer. Run the webbing through the bolt, tie to back-pack, and run.
If you don't want to pull with your back,Marshall's article tells you how to fashion a system for a waist pull: