I had my second shot on 8/30 (Friday). Friday night was fine, mediumish fever before bed though (around 99, up from my usual just shy of 98F per my doctor).
Saturday? All suck, all day, fever went to just over 101 after which I made myself stop trying to make sense, took more pills, a shower, and tried to sleep. Today the fever is reduced back to the mid 99s, but my energy comes and goes with it. Fever spikes? Frenetic energy. Fever drops? Exhaustion. Still, if the experience of my first shot remains true, I’ll be largely recovered tomorrow, which is why I scheduled the shot for a 3 day weekend. 
For the record, my wife, who did the same, felt moderately achy and warm Saturday, but that was it. She’s been very nice. So I’ll do the same next month when we get our seasonal flu and COVID boosters, which always lay her out, while making me feel just “under the weather” for 48 hours.