The heart knows its own bitterness. -Proverbs 14:10
R. Jannai said: If the patient says, I need [food], whilst the physician says: He does not need it, we hearken to the patient. What is the reason? The heart knoweth its own bitterness. -Talmud, Yoma 83a
The righteous shall live by his faith. -Talmud, Makkoth 24a
"The world considers faith a small
thing, but I consider faith a very great matter." -Rabbi
Nachman of Bratsalv
While it is important to listen to the physician, it is also important to listen to ourselves. Our bodies are designed to give us feedback on what is wrong, and this feedback should be paid attention to by ourselves and communicated to the physician. Thus is it written that "the heart knows its own bitterness."
Faith in Kabbalah does not necessary mean the same thing that it does in other religions. On the Kabbalistic Tree of Life, the letter "nun" is assigned to the path that connects the sephirah "Yesod/Tzaddik (foundation/righteous)" with "Netzach (endurance)". Netzach corresponds to the right hemisphere of the brain, and "nun" stands for "nehehman (faithfull)". Thus, the righteous person is in touch with his intuitive side, and he is able to enhance his health by listening to those messages and health alerts that come to us through the nonrational side of our being.