I get a feeling in my shoulder like i'm being stung by a wasp about 3 times a year, real sharp shooting pain. Pretty sure thats a trapped nerve somewhere, and put it down to having all my muscle ontop of my shoulder and non beneath (from trials). I also landed backwards onto a rock a few years ago and smashed my helmet to bits, and gave myself whiplash. Chiropractor said I have scar tissue where it should be muscle and that limits my head turning ability and my neck aches after a few mins looking down at a keyboard or whatever. I also fell off my mtb and landed on my arm which pulled it right around my front and stretched the muscle in my back / shoulder blade. That was 3 weeks ago and still hurts when I move my arm in a certain way or move my neck. A friend had what felt like back pain but was actually a trapped nerve in his arse / thigh zone.
When I started typing I think I had a point to make but I've forgotten what that was. Sorry.