Fear is a survival tactic that is built into our species. You are all familiar with the fight or flight syndrome, and that is where your fear originates. In the early days of mankind, the human body’s fight or flight syndrome was meant to protect you from the dangers in your environment. Today, however, your fears often center around emotions rather than physical dangers… although your body does not know how to distinguish between the two.

Source: The Psychology of Fear | Dr. Gail Gross