The other expert is offline and I will help you. It sounds like you have been through alot of medical investigations and that is good to hear. You have done the correct things so far. Underactive thyroid (hypothyroidism) can create the extreme fatigue, however that is being treated now. My other thought is about your oxygen levels and possible apnea. I would recommend wearing a pulse oximeter to measure your O2 reading and heart rate, but it sounds like that might have been what the Mayo clinic doctor had you wear already. If not, then I do recommend discussing with your doctor the possibility of wearing one. Next is the consideration of fibromyalgia or Epstein Barr Virus (EBV). This is determined from symptoms and specific blood tests. If the doctor has not done these blood tests, then please discuss with him. Both of these illness can cause your symptoms.
Please be well!
Thank you for your reply. Fibromyalgia is diagnosed after the doctor takes a medical history and is aware of symptoms, and then runs blood tests. There are certain tests results and symptoms, that when combined together, help the doctor make the diagnosis of fibromyalgia. There is not a specific blood test or x-ray that determines fibromyalgia. Symptoms are muscle aching, extreme tiredness, constipation and diarrhea, headaches, nausea and heartburn, sudden weight gain. Hypothyroidism can mimic fibromyalgia symptoms, and also EBV and high calcium. At this point ask the doctor if your blood calcium level was normal, as this would rule out hypercalcemia. When all else is ruled out, then the diagnosis of fibromyalgia can be made. Look at the website below and let me know if it helps you.
By the way, it is normal for cortisol level to be higher in the morning and then fall during the day, as you mentioned.