Thanks for your first question, Karin.
The brain’s danger signal is there to alert us to immediate danger, so it can activate at any moment. If our brain feels threatened by some event (physical or psychological), it can create pain or other mind-body symptoms. Most people have had some of these in their lives, whether they recognize them or not. I tell all my patients: “You are just human, and it’s human for our brains to warn us if we’re in some kind of danger.”
Clearly, some people have had many stressful life events that lead the danger signal to be sensitized and more easily triggered to create pain or other symptoms with even seemingly small stresses.
How quickly one can recover also varies widely as Alicia has pointed out!