The normal stress response slows when the hippocampus, deep within the neocortex’s medial temporal lobe, runs out of cortisol receptors and sends out messages to suppress corticotropin-releasing hormone (CRH), which inhibits the release of adrenocorticotropic hormone (ACTH) and cortisol. Suppressing cortisol production should result in the body moving toward a new state of balance or homeostasis optimal for health. As a result, the sympathetic nervous system will deactivate and the parasympathetic nervous system controlling normal functions will reassert its control.

This relationship between the sympathetic and parasympathetic (PNS) divisions of the Autonomic (not under conscious control) Nervous System reflects the body’s attempts to achieve homeostasis on a macro level. When the body is healthy, activity levels of the SNS and PNS divisions tend to reciprocate as would two children balanced on a see-saw—when one division’s activity is high, the other’s is low. The movements between the two divisions are fluid, measured, and can contain an exhilarating, but not frightening, spring. However, while traumatic stress can be only “stress in the extreme,” posttraumatic stress disorder is not merely an exaggerated or extreme normal response to exaggerated circumstances. Traumatic stress that does not develop into Acute Stress Disorder or PTSD is somewhat like two children of equal weight riding the see-saw as fast as they can.