I tried to follow the form in those videos tonight and wound up hurting a lot worse. In particular, the points at which my biceps and triceps connect to my humeri, both on the front and back, near the elbow, felt as though they had been severely strained, or otherwise injured. Though they calmed down after a few hours and some ibuprofen, they're still very sore. Definitely not nerve pain, this time, at least.
Much worse was a spot within my left shoulder. I'm unable to tell if it's the deltoid itself or a muscle beneath it, but it was sore and painful to the touch, much like a bruise is. Like my forearms, it's improved, but it's still sore, and poking at it is still uncomfortable. I'll see how I feel on Monday and, providing it feels safe, try again.