Just read your post on Mayo clinic, sound just like me...formerly very healthy, except I had thyroid disorder for 35 years that was very controlled with thyroid meds, no problems. I had covid almost 2 years ago, and was vaccinated 5 times.... and ever since have had terrible GI problems, Cardiac arrhythmia, Thyroid issues, brain fog, chronic fatigue, hair loss like crazy, like you. I also retired and my life has become doctor appts and test tests tests that don't show anything except low iron and higher cholesterol which is hard to believe as how can any food be staying in my body? I have loose stool many times a day. The theory is either covid OR the vaccine is the cause of all my symptoms, but no test for that is developed at this point. My thyroid was pretty much atrophied after so many years of thyroid meds, but Endocrinologist and Cardiologist were both convinced that it was probably still pumping out some thyroid hormone willy nilly and since I had covid it was making it impossible to get my thyroid hormone level right... if I had my thyroid removed it would make me better, so I had thyroid removed 2 months ago. For a few weeks I felt a little better, but then all my former symptoms returned! and I'm as bad as ever again. Now have to start the rounds of doctors once again to see if they can do anything, even just symptom relief, particularly the GI stuff which is horrible. Your message was from March, really wondering how your are doing now? any improvement or solutions for any of the symptoms? My sister who had covid when I did had the same symptoms but far less than me, she is convinced its from the vaccine as she had a vaccine about 6 mos ago and her symptoms came back but not for too long, she's a lot better now!