Back sprain.

Last Wednesday during warmups I noticed my back felt... tight.  Something was wrong but I had no idea what, so I persisted and did most of the calisthenics (skipped the ones which were obviously lower-back intensive) and then did class (which ended up being positional sparring for the next hour.)

One of my larger teammates offered to go a little heavier with me than usual because he was concerned that the local brownbelt who I outted might have other means of shutting me up in mind.  Of course, given that this person in question is a brownbelt, I'm probably screwed anyway-- but despite my back I accepted his offer.  And because my back was out, I couldn't even upa, shrimp, or escape with even my usual mediocrity.  So, I cowered and protected my face and generally endured.  Which was what my teammate wanted to see and show me-- even injured, even against someone twice my size, I can survive.

I really can't pinpoint what I did that cause my back to go out.  It's never done this before, and generally I think I have pretty good core support and fairly strong back musculature.  But whatever it was, my back did NOT like it.  By Friday I was really challenged to get out of bed or stand up from the toilet.  I had to miss a friend's baby shower on Sunday, and today I'm still hurting.  I will be happy if I feel like training tomorrow night; today is out of the question.

I'm going to set up a massage, hope that helps.  Otherwise I've done NSAIDs, hot showers, even tried muscle relaxants.  Foam roller and swiss ball have not improved things.