Weather and nutriture have been mentioned...
A few points I‘d like to emphasize:
Snow, water, sugar, preparation
Let it flow, let it flow, let it flow!
As a teacher I could always have been telling you when it will start snowing or when it was full moon.
If you are dependent or influenced by such variables you can really find out by a log book.
Also your biorhythm may play a role. You can have a look at it but don‘t exagerate it.
However the three most important points I didn‘t know or didn't care about at all before are:
Our body is like a plant. If a plant didn‘t get enough water it becomes dehydrated: your brain feels like dryed out, your body becomes sloppy, your fingers get stiff. A glass or 5 dl of water can prevent this state. Mind that water is not only important for the fluency and the blood circulation but also for the energy and electricity of the body and the neural system. I had 50 years to find that my „tinitus“ and my fatigue were often caused by lack of water.
Blood sugar level
Sometimes it is just a lack of sugar. When you‘re undersugared, you don‘t need speed, coffee or a coke! an apple will fit.
One thing I‘ve found out quite soon: the preparation. we call it „einspielen“, that‘s what orchestra musician use to do before the concert! You could say the readiness or the setting. There are lots of warm-ups for the mind, the hands and fingers.
What I didn't know for a long time is the benefit of mental training: you can practice it almost every where. this works in the bus, in the train but don’t do it in the car when you are driving: Imagine the chords, the fingersetting, the tune in solfege, visualizing the keys.
Otherwise you are like a booting computer or a hanging system lacking a software update. If a shut down won't help ... try a de-fragmentation of the hard disk.