I recently saw a well known arrhythmia specialist and he told me that we will always feel worse before we feel better when it comes to working out. He told me that it will take a while before the intolerance goes away. He said that is why it is so hard on many of us because we feel so much worse at first it is hard to push through. He said if you can push yourself in the long run it will make a huge difference. Your heart rate will slow down and we "should" feel a reduction in overall symptoms. That is for those of us who just have POTS. Swimming I heard was a good option and Pilates. Until you build up muscle, but cardio is key. You need to strengthen your heart. The doctor told me it can take up to 6 months before we feel better. I am struggling myself and trying to get on a more structured plan. It is so easy to give up, which I have many times, because I feel awful after I start working out. Usually later at night like you, I found I cannot work out past 3, if I do I get very symptomatic at night. I read that some places offer a cardiac rehabilitation program, like the mayo clinic. I wonder why they don't offer that to more POTS patients. Hope this helps!