I should have known that trouble was coming yesterday afternoon, when I was walking around center city. Nothing that happened, just a fatal thought: "you know, I've really been very healthy lately."
By ten that night, on an otherwise normal train ride home, I realized that my right hamstring had knotted up. Didn't seem anything that troublesome, more like a cramp than anything else. It just hasn't gone away, though.
I'd been planning on doing some speedwork today, but decided not to.
Status: no pain, some tightness. To be monitored.