Well, whatever it is, it is probably time to take a rest.
I have had this before, and whilst it might be a technical problem, it could also be down to over practising.
You say you are not looking for a teacher, but i think you should do so without delay. You might have developed bad habits which will take longer to cure the longer you leave it.
If this continues even with rest, i would be obliged to see a doctor to rule out trapped nerve, carpal tunnel etc..........
Thal