It is often said that the only constant in life is change – in fact, responding to change might be considered the most fundamental aspect of life. As early as the 1930s, Selye used the term stress to refer to any condition (perceived or real) that threatens homeostasis (Selye, 1952, 1978), or in other words, signals the need for adaptive change. Responses to stress signals are believed to have developed as an alarm system for animals caught in a potentially dangerous situation, and as an activation system for animals faced with a competitive situation. These physiological responses to stress are coordinated by a rapidly responding sympathetic nervous system (SNS), and by a slower but longer-acting second stage involving the hypothalamus, the pituitary gland, and the outer cortex of the adrenal glands (collectively termed the hypothalamic–pituitary–adrenal axis, or HPA; Lopez, Akil, & Watson, 1999). Restorative biological processes (e.g., digestion, immune function, tissue building) are temporarily suppressed so that energy resources can be mobilized for activity (Sapolsky, Romero, & Munck, 2000). In the extreme, the stress response becomes a stereotypical set of behaviors and physiological reactions initially described by Cannon (1932) as the “fight or flight” response. Generally the physiological reaction returns to baseline levels soon after the offset of stress cues. If a stressful situation is prolonged or inescapable, the initial high state of physiological activation cannot be indefinitely sustained – eventually, exhaustion sets in.