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

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. ​ Here is an example: You are hiking and you see a snake. You jump back, your heart is racing, your breathing is shallow, and you begin sweating (short route, no thinking). A moment later you determine that it is a harmless garter snake (longer route, fully assesses threat). Your heartbeat begins to slow down, your breathing returns to normal, and eventually you are calm again.