Deep breathing is linked to positive emotion and the ability to manage anxiety (Borkovec & Sharpless, 2004).
Reference: Borkovec, T.D., & Sharpless, B. (2004). Generalized anxiety disorder: Bringing cognitive-behavioral therapy into the valued present. In S.C. Hayes, V.M. Folette, & M. M. Linehan (Eds.), Mindfulness and acceptance: Expanding the cognitive-behavioral
tradition (pp. 209–242). New York: Guilford.