Mind games

To what extend does the mind rule what's going on in your body?
I've been battling with that question lately as I've experienced a period of discomfort that seems to have no medical (physically) basis.
Through a bunch of tests over several months I have been continually told `there's nothing wrong' yet the symptom still remains. It settles for a while then returns at unpredictable times (one of those being the recent present).
I'm no stranger to a bit of health anxiety but, on the whole, I haven't felt particularly anxious for a while, at least not consciously, so it is all a bit strange. This episode has only served to highten my awareness of such issues.
So I wonder whether there is a part of the mind that is causing this. And assuming it is, how do I get it to settle down?
As I said a while back I tend not to pray for myself too much, at least I try not to, and always leave myself until last. Perhaps this is serving to teach me something. If there is nothing symptomatic of anything remotely serious (that I don't already know about) that should be enough to settle the mind. But perhaps I've been so shaken up by everything that has happened this year I am yet to completely settle down. I hope it is that simple.
I think I am pretty good at perseverence and I know that God doesn't test you beyond what you can handle.