I would say that thyroid problems can have a substantial impact upon POTS. About a month before I was supposed to start law school my BP became dangerously low and if I even attempted to stand up I would immediately pass out. My blood pressure was 50/30 and my heart rate was about 160. I literally had to crawl to the door of my apartment in order to let the paramedics in. I thought that I was just experiencing an incredibly severe flare of POTS at the time but I could not figure out why it was happening. I had not had any medication changes, was staying well hydrated, etc. My primary care doctor hospitalized me, did a vast array of blood work, and determined that my thyroid gland was not producing sufficient amounts of thyroid hormones. He diagnosed me with hypothyroidism. He put me on synthyroid, synthetic thyroid hormones, and my blood pressure and heart rate returned to "normal" (well at least normal for me). In a matter of 2 days I was back on my feet. I had no idea that thyroid problems could affect BP and HR so dramatically. About a year ago, my thyroid started making sufficient thyroid hormones again and I was able to get off of the synthroid. The doctors still have no clue as to why my thyroid stop producing hormones especially since I have no family history of thyroid disorders. My recent labwork indicates that my thyroid hormones are on the very low side of normal and I am wondering if that could be the reason for my current POTS flare up. I have an appointment with an Endocrinologist next week so I am hoping that he is able to help me.