Ok, I might be a bit intolerant these days, since I have been diagnosed with ulnar nerve entrapment recently
I'm sorry to hear this--I had this problem as well....
I did too.
It was when I came back to working intensively on piano after some years away from it. I figured it was something about how I was playing
....I mean not just how much I was playing.
And it wasn't hard to figure out what it was (with my teacher's help). It seemed to be something about a particular position I was putting my hand in (it was just one hand), and a couple of particular pieces were bringing out, and certain passages. I made sure I avoided doing that, which also meant changing some fingerings -- and I got better.
Oh -- I also wore a wrist brace at night for a few months.
I don't mean to say that everybody's ulnar nerve entrapment (or carpal tunnel syndrome, or whatever hand problem) is that simple. But I'd bet a lot of people's hand/arm problems that are treated with physical therapy and/or medications and maybe even with surgery could be taken care of more simply -- and more meaningfully -- by looking for this kind of thing, whether we're talking about piano keyboard or computer keyboard, or any other kind of repetitive manual activity. The input you gave Hakki is a good example of how to start approaching it, although I think it's hard to be able to be that specific from afar.
I wouldn't be that quick to advise seeing a Taubman person, because from what I've gathered, all too often they tend to be a "one-note-Johnny" -- they feel the answer to everything is just to adopt the Taubman method. That might well work, but not as directly as just looking at what specific thing it might be about what the person is doing. It might not need a total overhaul of how he plays -- which is what I think the Taubman person would usually try to have him do.