It's like the body reaches a false equilibrium in which the injury doesn't heal completely unless you "knock it out" of the equilibrium again. From personal ex

It's like the body reaches a false equilibrium in which the injury doesn't heal completely unless you "knock it out" of the equilibrium again. From personal experience: if you have mild pain from past injury/strain, don't give up on trying to fix it. Move a lot, improve your muscle strength and try to stimulate circulation. Be careful not to repeat the injury, but don't avoid the pain altogether (eg. by reducing the amount of movement). It's possible that the pain will improve or disappear, even if your injury didn't heal by itself for years. (Oh, and go see a physiotherapist a couple of times if you haven't already.)