Pain is defined by the International Association for the Study of Pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage" (Merskey and Bogduk 1994, pp. 209–214). Acute pain, usually occurring in response to identifiable tissue damage or a noxious event, has a time-limited course during which treatment is aimed at correcting the underlying pathological process (if any such intervention is deemed necessary). Chronic pain, generally considered as pain persisting for longer than 6 months, may or may not be associated with any obvious tissue damage or pathological process. In the case of chronic pain, presentation may be characterized by maladaptive protective responses or pain behaviors, protracted courses of medication use and minimally effective medical services, and marked behavioral or emotional changes, including restrictions in daily activities. Pain-related avoidance behaviors and reduced activity are likely to result in a cyclic disability-enhancing pattern. The longer pain persists, the more recalcitrant it becomes and the more treatment goals focus on improved coping with pain and its concomitants (Kulich and Baker 1999; Martelli et al. 1999a). Finally, there is increasing evidence and growing acceptance that persistent pain may be associated with peripheral sensitization or central sensitization effects in which hyperresponsiveness or spontaneous discharge of components of the pain system develops (Lidbeck 2002; Nicholson 2000b; Nicholson and Martelli 2004). In this regard, it has been noted that there is an association between posttraumatic stress reactions and the development of chronic pain (Bryant et al. 1999; Miller 2000; Sharp and Harvey 2001), with uncontrollable pain after physical injury potentially representing the core trauma, resulting in posttraumatic symptomatology (Schreiber and Galai-Gat 1993).