I play pretty much every night, either at home or league. What I've noticed is that my consistency pretty much follows how well I'm able to focus on what I'm doing. Unfortunately, I played for lots of years just banging the balls around without really focusing on all the fundamentals that lead to consistency, so it is really easy for me to slip back into that mode. I still do that kind of intentionally prior to league play or at home when I'm playing less skilled players, just shooting fast and loose. It can get kind of scary how consistent I can be after playing that way for a few games, but for league, I really need to slow down and pay attention. I think it's the nerves that come into play as well as the down time between games/matches. If I remember to slow down, I do okay, and I can do okay sometimes playing fast and loose, but I can also frustrate myself to no end jawing point balls in the pockets.
I've also noticed that if I'm very tired it can have a negative affect on my game. As I focus more on focussing (LOL), my bad nights are getting fewer and farther between.