Alright so Ive been playing about 7 months or so and thus have developed some decent callous on my fretting hand. The other night I was playing longer than usual and all the sudden i fretted a note with my middle finger and got a really sharp pain. It felt almost like a paper cut except there was no blood or any sort of mark I could notice. I couldnt use the finger for the rest of the night and the next day I still felt a little bit of discomfort. About 3 days later the discomfort went completely away and everything was back to normal so I was wondering what this possibly could have been and if this happens to anyone else

Random question, what keys are Metallica's One and Fade to Black in? Thanks