Justjules, all of that seems so familiar. My heart would jump to 120 out of nowhere, I had no energy or motivation, and felt like I had no endurance to walk, sometimes even 50 meters seemed too much. Event thought the doctor assured me my heart was fine, I couldn't get over the ideal that he may be missing something. The hrt has helped significantly, but I still have blips of feeling like I can't handle any exertion. One thing that helps me is knowing that on good days I can handle aerobics, hiking, jogging, etc and have no issues at all. I feel like if it was anything besides hormones, I wouldn't have days that I can really exert myself with no problems. I wish every day was a good day. Heat intolerance has been another big one for me. Sometimes the heat seems to make it worse and sometimes it doesn't bother me at all. I know for sure my thyroid is under control, so I'm thinking it has to be the hormones.