Took another complete day off to heal this back injury. I'm taking a muscle relaxant--along with some pain killers--and the thing is getting better. Still very stiff and sore, but not debilitating. My plan is to take today through Sunday off completely, then ease back into my regular routine on Monday.
Meantime, I've registered for the Monumental, and I've tried to learn a lesson from this injury by planning better core workouts. I've ordered what looks to be a useful guide to core exercises, and I'll put into place a core regime next week, on my running days off (Tuesdays and Fridays).