I think I have a similar thing that happens to me. I get pain that almost feels like weakness (but my strength is normal) in my right arm, mostly wrist & below the elbow, but sometimes it's in my upper arm, too. This has been happening on & off for a few months now & over the weekend, it happened in my left arm. Anxiety & stress DEFINITELY make it worse. I think my problem is that when I'm really stressed I tense up in my neck & shoulders & I think it pinches a nerve or something. I have a friend who is a massage therapist & she said holding tension in your shoulders can definitely cause arm pain, "weakness", pins & needles feeling, etc. It certainly wouldn't surprise me if there was some sort of connection with tendons, as well. It's insane how closely everything is connected.