I think (personally) that the rebound crash the next day or hours after exercise (what they call payback maybe) is an autoimmune/inflammatory response or just the mechanism worsening after exercise for what ever reason. I find that at first after a crash any exercise makes me worse but I do gradually get better if I persist. the best way to avoid the payback is to keep going before it comes back. For me its either complete rest or exercise. If i exercise and then take the foot off the pedal i go backwards. that being said I am in no way implying that exercise is a 'cure' for pots or even that effective a treatment. When i was running 5kms three times a week, swimming 1 km twice a week and doing weight training Id still require licorice to get through the working day and I relapsed just as much. For me at least exercise just seemed to improve my ability to exercise without getting worse. It increased tolerance - just like if there is a food that makes my pots worse I can avoid it or eat it constantly until my body gets 'over' its weird reaction it all sounds crazy but after 11 years these are my conclusions.