We have all experienced stress; in some form it is a survival tool that gives us energy and fuel to handle a pressing situation. Sometimes a stressful situation is so overwhelming that we will do anything to avoid that situation for the rest of our life. In these cases, our security system will code everything in that situation into a script that will trigger a stress response as soon as anything reminds us of it. That stress response will grow stronger as our system generalizes it, to the point where we can generate a full life-or-death panic response by simply thinking about it. It is then called post-traumatic stress.