Smash and Grab

Since I got into furniture construction and restoration, people have insisted that This means I must be able to do construction. Now, true or not (and, as it turns out, true--I've worked in the field and also had some formal training), furniture and construction aren't the same thing. One is intense shop-work and the other, well, isn't.
Well, apparently I've embraced my inner carpenter, because I've taken on the project of renovating a basement. Today I started, and I started by tearing out the crap that was in the basement. Used as both bedrooms and an indoor garage, I had to tear out cobbled-together walls and pull out nails by the kilo.
Clearly the basement was used at some point by teenagers, as one of the things that turned up under some other stuff, was a very small and very well-used hash pipe.
Bashing things up went pretty well; by 2:00 pm I had most of it taken down and was starting to de-nail and stack the waste. My lower back was indicating that I hadn't used it in this way in a while and it was starting to get tired of swinging a hammer and wrecking bar. Most of that was done, so I was fine with that.
And then about 3:00pm, I was unloading some of the wast sheet goods when I felt the muscles in my right arm go. I'm not sure what I did, but there was pain. And, most frustratingly, it didn't go away. And didn't go away. And hasn't gone away. I really hate this--pain is supposed to happen, you stop what you're doing, and the pain goes away. At the moment, I'm having trouble straightening my right elbow, and muscles are complaining all the way up to my shoulder. But primarily it's my elbow. What the hell is next? I'm getting pretty tired of breaking down just when there's things I actually want to do.