I think the most important thing is to understand what went wrong on bad days. That's how I found out that not only does a drop in my blood sugar levels (hereditary problem) affect everything but also a drop in my electrolyte levels affects my reflexes, timing and coordination, too.
So now I try to drink sports drinks with glucose on odd game. Hange-overs, but I also make sure to eat a meal with lots of complex carbohydrates 2 hours before I play.
I still have bad days but now it's because I play stupid without realising it, e.g. hitting a 3/4 court forehand and then running to the net AND mot doing a split step to prepare for the return either.
5' 10". 55. Fat. No talent. I'm ONLY 3.5 no matter what anybody else says! And GOATS have horns, eat grass and go "Meh eh eh eh!"