One theory for the effect of NFB is that it replicates the twilight states of the brain, the hypnagogic and hypnopompic states of going to and coming from sleep. The theory is that the brain does a lot of "figuring out" emotional issues and trauma in those states, and that inducing or prolonging them is helpful.
Digestive health has way, way more effect on mental health that many people realize. An ounce of Metamucil is worth a ton of neurochemical intervention.
Mindfulness is hard. Oh, you knew that, though.