When I had flu a few years ago, I was off work for 2 weeks, and couldn't get out of bed for the first week. When, the second week, I managed to crawl to the doctors, the doctor told me that she saw dozens of people a week with what they thought was flu, but it was in fact a heavy cold. She said I actually had flu, and signed me off for a further two weeks, and told me it would take a further month for me to feel completely better. And it did.
A couple of months ago, before all the current measures, I had a virus that now I think probably was Covid. If it was, it was no where near as bad as the flu described above. But I don't know, because I didn't get tested. I think anyone, with or without a test, even if it was positive, should behave as if they haven't had it - social distancing, hand washing, etc. I would say that if I had Covid, it was more similar to how I felt during and after shingles, rather than flu. Just my experience. Following shingles, if I was run down, stressed or unwell with something else, I would have a 'flare up' of shingles type symptoms. I really wonder whether Covid could stay in the system like this, and flare up again later. Just my musings.
I now have a flu jab every year, but am still worried about getting it again. I do all I can to boost my immune system, keep my weight down, etc., to boost my chances. I would like to see more emphasis on weight control, healthy eating and boosting immune system generally. Whether we get Covid or not, it won't do any one any harm to improve their health generally.