Hi Dantheman, doesn't sound like a ganglion to me. Your comment about the guitar is rather interesting. Is the left the cord playing hand? If so the extensor muscles in the forearm are used a lot when playing guitar. And having someone take a look at the way you are playing may help with that.

I'd be getting the neck and whole upper limb checked to see if there is any observable weakness that could be causing abnormal fatigue in those muscles. One needs to look for the root cause of your issue here. The computer is probably more a secondary activity that is provoking the symptoms.

A good physio / osteo / chiro should be able to make an assessment and advice plan for you in one visit. I'd suggest it and do let us know if you do that and what they found or suggested. Best of luck p.s. Having been the City Of London Police fitness advisor and occy health PT I would not think that this issue should prevent you joining the force