I went through all the tests for almost 3 years. It took a long time to diagnose my issues. It was a long frustrating process. I am now with a long COVID clinic. My dizziness continued to get worse. I have to wear an abdominal binder or I black out while sitting or standing. Through the long COVID clinic I have been diagnosed with POTS and COVID is attacking my autonomic nervous system. I would recommend seeing if your friend can be referred to a long COVID clinic. I would also recommend in the mean time seeing all of his doctors. I would also recommend trying compression socks or an abdominal binder to help with the dizziness. Part of my long COVID is extremely high anxiety. I can't take anti anxiety medicine due to the medicine I take for neuropathy. Through a physical therapist who specializes with this, there are only a few, I have learned breathing exercises that help me calm down. I would also recommend that your friend not try to exercise. I recommend not doing things that increase anxiety and frustration. For years I would have to nap after getting up and taking a shower. Unfortunately Long COVID does impact your energy level and cause exhaustion. I can now only do 20 minutes of anything physical, for me that is laundry or washing dishes. I don't have any heart damage and it did not damage my lungs. I was told by my Long COVID clinic coordinator that what they are seeing is that COVID is turning on all of our bad genes so not everyone will have the same symptoms or have more or less symptoms. I wish him good luck. I hope he can be diagnosed and find help much faster than I did. And hope he can find a way to relieve his anxiety. Mine was so bad that any little thing had me in an anxiety attack and hyperventilating. I really thought I was losing my mind. Let him know he is not.