Best wishes for a speedy recovery, Gary.
I think this virus is like the flu (bare with me) but more like the kind of flu someone with health conditions can experience. As an asthma sufferer all my life a basic cold can mean a couple of weeks of antibiotics, steroids and double inhaler use, no work and a lot of sitting around with no energy for anything struggling to breathe. But something like pneumonia, which I've been in hospital with, felt like someone had smashed my ribs and I was in an ambulance 30 mins later in the middle of the night. What you are saying reminds me of that.
The temperature issue reminds me of a mate years ago who had flare ups of the malaria he once had. He would go off work for a week and sleep on a radiator to sweat it away.
So healthy people might find themselves struggling more because it has the power to inflict a more advanced illness. So then adding that to existing health conditions, as you say, is just piling more on top.
Get well soon.