I didn't do any heavy lifting yesterday or anything else that could have strained my back. I guess I just slept wrong. This has happened a couple of times before, although not recently. It will, I think, work itself out eventually -- it's just a muscle strain of some sort, I expect -- but it means I can't go exercise much because walking is such torture.
If there hadn't been things I needed to do in the office today, I would have worked from home. I'll be working from home tomorrow anyway because I need to be able to leave with enough time to take BART up to Berkeley for a 7:30 PM meeting I have with the other members of the SMOFCon Scholarship Committee. If this back pain doesn't let up, that's going to be a very difficult trip for me.