Personally, I had Covid at least once (found out via a blood donation) with no symptoms at all, this was before vaccines in Nov 2020. I then did the J&J in Mar 2021 at noon on a Friday and was very sick, like in bed and miserable from when I woke up feeling terrible at 2AM Saturday until Monday morning. Sunday night I thought no way I would be able to work Monday, but by morning I was 85% better. Then I was fine until I got the Pfizer booster in Nov 2021, and it was same thing - I scheduled it for a Friday afternoon and felt fine until early Saturday morning and then was sick and miserable until Monday morning. I then got the bivalent booster in October 2022 and it was the same thing (3:30pm appt) except Sunday was not quite as miserable, I was up and able to do a bit but felt bad. I have no idea why this happens, I have had annual flu shots, I did the old less effective shingles vax and then later the better 2-dose shingles vax, etc and have never had any side effects from any vaccine. If I ever had Covid a second time I had no symptoms. The rest of my family members did not have side effects (after the original first shot my wife didn't feel great on the day after, but still worked), especially my extremely elderly parents.