My household all got covid over Xmas (brought home from school by DS). We all had the mild, flu-like version, wouldn't recommend it but never felt like we needed medical help. 4 weeks on everyone apart from me is out the other side. I went back to work as normal but found the fatigue, brain fog, lack of concentration and muscle weakness and shakiness on the slightest excertion too much. Still have lung pain and a slight lingering cough, but actually they aren't the debilitating things. I've been put on antibiotics and told to rest.
What this feels most like is uncontrolled hypothyroidism. I haven't found any info about the effect of catching covid on hypothyroidism (some the other way round), and wondered if fellow travellers wanted to share?