Update --- so the days I was really tired after riding, I'd attempt to nap. Really just laid out on the couch. After a few hours of dragging a$$, I get to the gym and roll my legs on a black foam roller. I'll spend about 10-15 minutes rolling followed by stretching. Then I'll lift weights (nothing heavy). Deadlift, military press, bench, maybe leg press. When I'm finished in the gym, I'm close to feeling 100%. Mentally and physically. My energy level is way up and stays that way until bedtime.
I don't know much about sport science, but I'm wildly guessing the acid built up in my legs after a ride is causing overall body exhaustion. Rolling, stretching and lifting is helping speed up the removal of the acid. Does this idea hold up with current views in sports science?
I'm going to do a ride tomorrow morning, refuel and relax for an hour and then hit the gym. I'm interested in seeing what my energy levels are like during the rest of the day.