I've had 4 shots, all Pfizer. I got the initial Pfizer 2-shot, and all except the first shot took me out for half a day. I always felt fine the day of the shot. The 2nd shot just made me feel really tired the next day, but after a couple of naps I was fine. Shots 3 and 4 (the bivalent) both woke me up at night with fever and chills. The 3rd one made me nauseous enough I booked it to the bathroom and dry-heaved a bit over the toilet. The 4th shot also made me feel a bit nauseous, but not as bad. Looking back at it now, the last two shots wer probably 2-3 hours of fever and nausea, then back to bed to sleep it off, but at the time I felt like hell and it seemed like it lasted forever.

I'm getting a flu shot next week. It was recommended not to do them at the same time because if there is a serious side effect, you won't know which one caused it. I've only had one side effect from a flu shot in my life. My arm from the shoulder to halfway down my forearm developed red speckles. That was it. It didn't hurt or itch and it went away after a day. It wasn't like a rash on the skin, it was just little red speckles under the skin.