I’ve seen it compared to the gulf war syndrome which happened to returning soldiers, a similar thing they spent forever looking for a cause (gas attacks etc) and never finding a physical cause. They determined it’s something that happens to people after a widespread traumatic event. Like a minor version of PTSD.

I’d love to see a study that took long COVID people and got them to do daily cardio exercise, go outside into nature, and sleep better (ie not over sleeping) and seeing if the symptoms improve vs a placebo group that sits inside all day reading doomer posts about COVID on Twitter/Facebook.