According to Polyvagal Theory, what specific physiological state is associated with complete shutdown or collapse in response to overwhelming threat?

According to Polyvagal Theory, the specific physiological state associated with complete shutdown or collapse in response to overwhelming threat is dorsal vagal shutdown, also known as immobilization or the feigned death response. This state is orchestrated by the dorsal vagal complex, an older, unmyelinated branch of the vagus nerve responsible for regulating primitive visceral functions. When an individual perceives a threat as inescapable and overwhelming, the nervous system triggers this most ancient defensive strategy. Its biological purpose is to conserve energy, minimize pain, and increase the chances of survival by making the individual appear unresponsive or dead. Physiologically, dorsal vagal shutdown is characterized by a significant decrease in heart rate, slowed and shallow breathing, lowered blood pressure, reduced muscle tone leading to a feeling of collapse or immobility, and often a sense of dissociation or emotional numbness. This involuntary response is the lowest and most primitive in the polyvagal hierarchy, activated only when the more evolutionarily recent social engagement system and sympathetic fight-or-flight responses are deemed insufficient or have been exhausted by the perceived threat.