Yeah I definitely feel like I manifest the symptoms of whatever I'm worried about.
When I was worrying I had testicular cancer, the pain in my testicle was unrelenting. As soon as I had an ultrasound and got the "all clear" diagnosis, the pain ceased almost instantly.
Plus worrying all the time makes me feel run down and generally poor, which in turn gives ammunition to the fear that I have some type of sinister disease, because let's face it, "feeling fatigued" is a symptom of just about everything, right?