Yes, I've thought symptoms had disappeared, and then they return just when I'm feeling calmer. Its happening at the moment, actually, too. Then on the odd occasion I forget or distract myself with what's happening, I suddenly get some symptom or another thought about it, and then I feel stupid for forgetting about it. And then the worrying starts afresh.
The trouble with most physical symptoms is that they can be attributed to hundreds of different ailments. This can mean that you're forever thinking you have a particular disease, but it could also help with dispelling those fears. I try to tell myself that any aches and pains could be over 100 diseases, and therefore I can't be expected to worry and can't physically be able test myself for each one, so ultimately I try and force myself to worry that I have a multitude of diseases at the same time. This somehow seems to overwhelm my worry, giving too much to think about, therefore I can't focus on any one fear. Its a bit like setting off a fireball to extinguish a fire. It doesn't always work, but often it helps.