Got Pfizer, and both shots were simple.
First shot, my shoulder was a little sore at the spot the needle went in, but no different than I remember any other shot being. No major side effects at all, really. I was a little tired the next day, but nothing too harsh at all.
Second shot felt like nothing happened at all. Although to be fair, I was pounding water through most of the day since I heard staying hydrated is key.
I think it's a matter of what your immune system is like, though. Mine might be pretty good, since I usually don't get the flu vaccine (because I hate needles), and I rarely if ever get the flu, and when I do, my symptoms are pretty mild. My lady on the other hand.....first shot hit her like a mack truck. A day after we got the first shot she started feeling effects, and was cooked for maybe a day and a half. It wasn't anything alarming, just like she had a pretty tough flu.
I'd say if you're concerned, try to schedule it around your weekend so you already have time off to handle whatever side effects you may or may not have. Anxiety over having other shyt to do on top of medical paranoia is a hell of a one two punch.