Grade: 3
Wicked muscle spasm from shoulder to kidney on my right side. Difficult to drive, agony to try and sleep. Gradually abated over the course of a couple of days (no difficulty running 48 hours later), but not before I managed to burn myself with a hot-water bottle.
Just waited it out. Application of heat felt good, but I don't know if it helped. No idea why it happened, though two days earlier I did do a bunch of hauling around of wood (Mom's yard cleanup).