Personally, I think in order to solve this paradox we need to know a few things. We need to know if destiny is a being or a force. We also need to know if destiny can be challenged, whether it's a force or a being. We also need to know if this "doctor" can challenge destiny, and if destiny has "people" to execute this "master plan." If destiny can be challenged, and is a weak force or a being, chances are yes, you could get well again from visiting a doctor. If destiny cannot be challenged and is a strong force, then no, it would not do any good to go to a doctor. Overall, this is would simple paradox (well not even a paradox, just a question) to solve, if we have just a bit more information.
-Samson
Also, is it our destiny specifically? Or everyone's destiny?