A symptom of leg problems is interesting as before my lurgy took a hold over late December, I was coming back from the local shop and found that my legs didn't want to go the few yards further to the front door and clearly remember visions of wanting to sit down on the pavement there and then.
I struggled putting one foot in front of the other before I got inside and felt like collapsing. At that point I had an idea that it was my chest/lungs which were affected because of a blip in circulation to the lower half of my body as lack of oxygen can cause these symptoms. Increased temperature only for a couple of days prior to a worsening condition.
Sure enough, I then felt as though there was an elephant sitting on my chest restricting my breathing and this went on for over a week with an irritating cough where I couldn't get my breath. All through January and most of February I didn't feel as though I " belonged ". Because my blood oxygen has always been good and had measured 98% for as far back as I can remember, I managed to fight back, but anyone with a poor lung/ oxygen function I feel heartily sorry for. Blood oxygen is ideally 100%---fit and healthy level.
Ironically I'm a smoker too !! I didn't call a GP, neither have I since seen one but slightly concerned at any damage that may have been done to the lungs though I haven't been gasping for breath and can breath freely, even experimenting going to sleep with one pillow, no problem.
Taichinan, as you say, testing should be vital as right now I'd be interested to see results of an antibody test just out of curiosity.