Equanimity means not reacting to your reactions... and that is both a wonderful relief from upsets and traumas, and a profound resource for spiritual growth.
In Buddhism, equanimity is one of the four Brahmaviharas (Divine Abodes), and is often considered the foundation of the other three: compassion, lovingkindness, and altruistic joy. Equanimity breaks the chain of suffering by helping you not react to the pleasant/unpleasant feeling tone of experience with craving and clinging.
Your equanimity, a state of mind, is based on underlying states of your brain. Modern neuroscience is revealing new ways to cultivate those brain states--a potent combination with time-tested Buddhist practices.