Rav Soloveitchik wrote that he was troubled when people said that being religious gives one peace of mind. On the contrary - being religious requires one to deal with the many dichotomies of life and often engenders emotional and spiritual angst. Just because you are religious doesn't mean that life is simple. We live in a fractured world and one must own up to that.
After mechilah from the great Gaon HaRav Yoshe Ber, it seems that the Chovos Halevavos in fact makes that very claim. Be truly religious and you will have peace of mind, calm and tranquility. Here is a link to a translation of his words.
May we all be zocheh to menuchas ha-nefesh. BYE-BYE XANAX!! [Great scrabble word:-)]