This a good diagram of the positive feedback loop that arises when someone starts to perceive the unpleasant physical symptoms of the Amygdala response as "dangerous" or "threatening".
The production of the signal (unpleasant physical sensations) eventually affects the levels of its own production. Which ultimately leads to a full blown panic attack. The production of the signal is increased by both classical (stimulus pairing) & operant conditioning (reward based).
Now any time you have similar unpleasant physical sensations arise.... the Amygdala is triggered automatically.... which produces even more of the unpleasant physical sensations. Its a vicious cycle as long as the sufferer continues to perceive those initial unpleasant physical sensations as "danger" or "threatening".
The way to break out of the positive feedback loop is to expose oneself to the unpleasant physical sensations, and view the unpleasant sensations as only causing "discomfort". Doing this stops the 2nd Fear feeding back into the Amygdala (1st Fear). Remember the 1st Fear is unconsicous, the 2nd Fear (perception) is the conscious response.
An Amygdala Hijack lasts around 18 minutes, but a total of around 4-5 hours to completely leave the body. So a sufferer needs to at least perceive the unpleasant sensations as discomfort for those first 18 minutes of a hijack. Once the 18 minutes have passed the sufferer may start to feel much more comfortable with the stimulus. However, if the sufferer decides to avoid the stimulus using safety behaviours the Amygdala emotional memory will be even greater the next exposure occurs. This is due to operant conditioning (reward based). By avoiding the feared stimulus the physical discomfort lessens, causing the sufferer to continue avoidance... Which only leads to a increase amygdala response the next time the feared stimulus is encountered.
The sufferer eventually enters a constant hyper vigilant state... Which further leads to classical conditioning (pairing of new feared stimulus).