Some days are better than others

There’s an old golf joke that goes something like this:
“Why is it that some days you can lose 6 balls in the water, hit every tee shot either into the rough or the trees, shank your iron shots, pull your fairway woods, and 3-putt every green - and then other days you just suck?”
I was feeling a bit like that yesterday when I was riding. It just wasn’t coming together. The corners didn’t flow. Shifting wasn’t smooth. And stopping at a traffic light… well let’s just say I’m sure other drivers thought I had just got my license by mail-order that morning. In short, I felt as awkward as a fish on a bicycle.
It doesn’t happen often, but it’s not uncommon either. Why is that? What is it that periodically (and, fortunately, temporarily) causes our bodies and minds to seize up like a grease-starved wheel bearing? And then, a while later, and for no discernable reason, everything pops back to normal as if the reset button were pressed. I wish I knew.