A curious idea you have here, and one I tend to agree with. I’ve often experienced psychosomatic symptoms (headaches, stomachaches — the usual suspects) in my own body, probably because I tend to fall in the crowd that views stress as harmful (sounds like I need to change that, stat!).
With physical pain (such as knees), I wonder if a pre-existing injury or trauma must exist for the mind to cling to it. Or, are our minds capable of creating this discomfort out of thin air? If so, do you think the type of emotional or mental blockage we are experiencing dictates the type of pain we feel?