Proper flu as in temp of 40deg and unable to get out of bed, having to crawl to the loo and with periods of being almost delirious - twice in my life.
Once in my 30s, where that stage lasted for a couple of days then I gradually recovered.
Then I got Swine flu 15 years ago in my 40s ,was very ill , unable to to get put of bed with periods of deliriousness lasted about 3-4 days then I was just feeling very ill but mostly in bed for a couple of days. Then just very very tired (as in having to sit down after coming downstaors tired) and having to convalesce at home despite most of my flu type symptoms having passed by then. Gradually got better but was off work for more than 2 weeks.
In neither case did I get many cold type symptoms - ie not congestion or runny nose etc. Both time I felt fine and then very suddenly, within a few hours I was unable to stand. Nearly fainted on the bus home when I had swine flu as it came on fro about 3pm in work during the afternoon
Other than that, I have the very occasional cold but really I almost never get colds any more - maybe once every 3-4 years (am 61 years old now). I did have Covid 3 times over about 2-3 years, the first time I fel very tired for a day then was fine except for a bit of a cough. The second time I felt a bit worse but nowhere near as ill as when I had the flu, then the third time I had no symptoms whatsoever, apart for a bit of tiredness one day.
DH on the other hand is ill almost every autumn. He teachs at a unoversity though so spends a lot of time with a lot of plague vectors students in Sept/Oct time. He has never had really bad flu where he really can't work at all though. If he is ill he does mostly manage to teach his classes though he might take a few days off in between if he is feeling particularly bad. He rarely hase very specific symptoms, just a lot of severe tiredness and sometimes cold symptoms