What happens when "Fight or Flight" is triggered... by a phobia?

When the brain receives a signal alerting you to danger, that signal is routed first to the thalamus, the brain's switchboard. From there, the information is sent out over two parallel pathways: the thalamo-amygdala pathway (the 'short route') and the thalamo-cortico-amygdala pathway (the 'long route'). The short route conveys a fast, rough impression of the situation, because it is a sub-cortical pathway in which no thinking is involved. This pathway activates the amygdala, which generates the acute stress response before the brain has even fully integrated what it is perceiving. This process is called First Fear (aka fight or flight) and you do not have control over it; it is automatic. A moment later, the information travels via the long route. Now the information is processed by the frontal cortex, which tells the amygdala whether or not there is a real threat. If there is no real threat, the acute stress response system winds down.In the case of a normally functioning acute stress response, when the information from the “long route” arrives, you are able to recognize that the situation is safe. The acute stress response begins to wind down. It might take several minutes, but your body will return to its formerly calm state. ​ In the case of a phobia, when the information from the “long route” arrives, you are already overwhelmed by your physiological sensations and you have catastrophic thoughts that reinforce that fear (e.g.,"Oh no, I can't breathe!"). You are literally afraid of First Fear and your reaction re-triggers the acute stress response. This re-triggering cycle is called Second Fear, or "fear of fear." When Second Fear happens repeatedly, a phobia develops.