Our nervous system is a miraculous and complex network of information and control mechanisms. Our SNS (sympathetic nervous system) readies us for action, to mobilize, to activate, charge, fight or flea..among many other things. Our PNS (parasympathetic nervous system) calms us down, soothes, relaxes, and regulates…also among many other things. So when we get stressed, frightened, angry, and scared we are feeling (and causing) our SNS to activate. The release of all of that emotion, in that moment of the big sigh we feel (and cause) our PNS to activate.
According to Dr. Stephen Porges in his book The Polyvagal Theory he notes that “Perceptions and assumed threats to survival, independent of the actual physical characteristics of the stimulation, may promote a massive withdrawal of PNS tone and a reciprocal excitation of SNS tone.” (67)
So if our nervous systems are responding independent of actual physical stimulation, the we are responding to our perceptions.