Bob Gollihur coined a phrase/acronym a long time ago - the "TZO." It stands for "Twilight Zone Occurrence." We use it regularly, whenever we just can't explain why something works (or didn't work, but now does.)
Every once in a while, your bass, your amp, or some other aspect of your playing world gets derailed by something that you can't quite explain. Maybe your bass develops a random rattle or buzz that you cannot locate. Or perhaps your amp suddenly won't power on, when it's been super-reliable for years, and you can't quite figure out why. It could even be in your playing; that etude that has fallen perfectly under your hands for years suddenly has you tripping over your fingers and making tons of mistakes.
But then, a day later, you come back, and things are working correctly again, like nothing was ever wrong. The rattle is gone, the amp clicks to life without any issues, and you're tearing through that etude like a virtuoso. All seems right with the world again.
And now, you're even more concerned. Without being able to reproduce the problem -- and not knowing what caused it -- who is to say when it might rear its ugly head again?
It's okay, you can probably relax. More often than not, this sort of thing doesn't come back. Hence: the "Twilight Zone Occurrence" (TZO.) It's a one-time phenomenon that defies explanation. We get them sometimes; a customer will call and try to diagnose an issue with their gear that they had on a gig or rehearsal. But since that one time it happened, they can't reproduce the issue, no matter how hard they try.
This is usually when I introduce them to the concept of the TZO.
Sometimes, when the explanations elude you, you just have to let it go and get back to playing. Spending too much time chasing phantom issues will just frustrate you and take your focus away from making (and enjoying) music. So if you've experienced a TZO -- with your gear, your bass, your playing -- try to shake your head, laugh it off, and move on.