Ergonomics and Wrist Strain
Playing and jamming difficulties...HELP ME!
I must agree with KenL. From watching your video here , your wrists are lower than your fretting fingers. It's actually the very same advice for computer ergonomics- elbows and wrists should not be lower than the hands/fingers when typing or mousing. This is to avoid wrist pain and carpal tunnel syndrome over time.
In that video, I see you are sitting on a couch that seems to put your seated hips lower than your knees. That positions the dulcimer on your knees higher up... which in turn causes you to have your wrists & forearms lower than the fretboard. I do recommend that wrists be higher than the fretting fingers, and elbows either at or higher than fretting fingers.
Perhaps this does not apply to your situation Nate, but I did a blog post that might have some useful thought in it about this. I wrote more about fingertip angles than arm or wrist angles, but they are related to each other.
If you are having wrist pain, you may want to examine your computer/device/phone ergonomics as well- they might be a contributing factor.