Even though the ride is stressful and challenging for each rider to keep up with the other, either can effect a change in the pace of the ride. On the other hand, stress that develops into PTSD is more like two children of very different weights riding the see-saw. For the lighter child, the ride up is too fast and the child fears flying off when the heavier child thumps to the ground. And then, try as the lighter child might, she may never get her feet back to earth without help. Likewise, in PTSD, the overwhelming demands placed on the autonomic nervous system when the SNS is called repeatedly into strenuous, but many times ineffective, action can unbalance the body to such an extent that its ability to respond to normal or daily circumstances becomes “broken” or disordered. While this disorder changes [perhaps forever (Friedman, 1997)] the course of the “play” between the SNS and PNS divisions of the autonomic nervous system, the disorder itself does not lead to the body’s death. An appropriate image for the effects of PTSD on the SNS and PNS relationship might be of a see-saw with the central balancing point for the fulcrum destroyed: Try as two children might, they will have trouble establishing a smooth and secure-feeling ride.

Stressors also affect the body’s homeostasis on a micro level, at the level of the neurotransmitter, in the push-pull relationship otherwise known as a negative feedback cycle (Seeley et al., 1995)^{Endnote 17}. A negative feedback cycle works (though not consciously) to avoid a crisis as a checks-and-balance system through which the body makes small, less dramatic, adjustments in response to its internal and external environment to maintain overall health. Failure to make the small adjustments early can result in a positive feedback cycle (see note 17), a cycle that requires intervention to forego possible disaster, even death. Sometimes, and current research in PTSD appears to point in this direction, the homeostatic midpoint shifts permanently in response to persistent imbalances in one direction or another (Morgan, Grillon, Lubin, & Southwick, 1997; Orr, 1997; Pitman, 1997; Pynoos, et al., 1997; Southwick et al., 1997; Wolfe & Schlesinger, 1997).