I can really recommend Breath: the New Science of a Lost Art, by James Nestor. One of those rare books that had a noticeable, positive impact on my life.
I also recommend that one. It made me always try to keep my mouth closed when i'm not eating or talking. Not sure though if it had impact on my health, but that of course might depend on where you come from.
It is simply lovely to watch from the sidelines as Western secular culture re-invents the Rosary, Hesychasm, and monastic contemplative silence as "mental health techniques" where God is expunged and superfluous.
Perhaps God never needed to be involved if people are returning to these practices sans theism and still gaining something from them.