To paraphrase Churchy LaFemme, "Friday the 13th come on a Friday this month!" My left shoulder started hurting, dunno what I lifted wrong, pushed wrong or slept on wrong, but it was bothering me whenever I reached for something the wrong way.
Woke up this morning, and my range of motion is much more restricted, at least without pain. I've been through this once before a year or so ago with my right shoulder. The joint just decides to get all tetchy. Course of treatment, as per Dr. Selby, is to slam it with NSAIDs (basically a lot of Alleve) and after a couple of days begin the gingerly stretching.
As my old high school chum Mike Wendell would say, "defective body, trade it in!"