Once the mind makes its decision that an event is stressful, the thought itself becomes our molecular reality in the form of biochemicals called catecholamines—the “stress” hormones that arouse key bodily systems to prepare for fight or flight. The brain, mindful of a crisis or a threat, signals the hypothalamus, which activates the master gland, the pituitary, which in turn activates the adrenal glands, whose hormonal secretions provide the familiar adrenaline “rush” symptomatic of the stress response. It is through the combined and protracted effects of these stress hormones on the immune system that thoughts have the capacity to make us ill.