The first good decision I made was to stop all work.
Next, I sought medical opinion. I was horrified to learn medical professionals were all over the place. I got recommendations spanning from surgery to vitamins.
I concluded that I'd do my own research and come to my own independent conclusions.
I focused on two areas: understanding the physiology or mechanics of the damage and taking a deep dive into ergonomics.
I came out convinced that the root cause was poor ergonomics. I had not caused enough damage to require surgery. I set out to test out various ergonomic products. Nearly all of them sucked. Gimmicky crap.
The ultimate solution was to design my own desk. The goal was to promote a fully relaxed posture with proper alignment and support.
The standard 29 to 30 inch high desk was designed in the dark ages for writing. Placing a keyboard or laptop on it throws your entire body out of alignment. Your fingers, hand, wrist, arms and shoulders end-up operating in tension as opposed to from a neutral stance.
My desk featured a dropped (about three inches) front section for the keyboard and thumb-operated trackball. I ditched the mouse as it caused too much tension. I found a thumb-operated trackball to flow naturally and comfortably.
A dropped keyboard shelf wasn't enough. The front edge got a solid piece of wood, 2x2 inches in cross-section with generously rounded edges. This created a forearm support across the entire width of the keyboard shelf. The net effect was that my hands very naturally drooped onto the keyboard and trackball. My shoulders were not unnaturally pushed up or pulled down.
I played with monitor height and settled for looking slightly down at the monitors (24 inch). I tend to alternate between sliding down in the chair and sitting up, which means that at times I am looking straight at the screens.
The end result was that all pain was gone and I could get back to work. I also took regular breaks every two to four hours based on flow.