Our brain when we're afraid

A perceived threat sends information to the brain's emotional processing and learning center, called the amygdala. The amygdala sorts out the data within tens or hundreds of milliseconds. If it registers the threat, then it fires off a series of physical changes. Heart rate, breathing, and sweating increase in the fight-or-flight response because the body is preparing to flee or to fight if escape is impossible.

Fear is the body's alarm system — it’s an innate emotional response to a perceived personal threat. 

 There are two different types of alarms, panic and anxiety, both of which are adaptive. Immediate threats activate the panic alarm, while anticipating a threat sometime in the future...