Have ever you watched children at play on the beach? There's often one child who spends all his/her time running around the castle protecting it from intruders of all shapes and sizes.
Operating in "protection mode" is not only exhausting, but also stress-producing. Danger or the threat of danger causes the body to go through a cascade of 1400 chemical changes which are designed for flight or fight. This was necessary for survival in prehistoric times, when it was action that was needed in order to deal with the beasts of the day.
Today, many of the things one fears or think one needs to fear doesn't come to pass - fortunately. However, being constantly on guard resets the nervous system so that it takes less and less to activate it. The window of calm gradually closes. Many of the defenses people set up to keep themselves "safe" end up wearing them out and down. They may be afraid to experience joy because "something bad is just around the corner."
I understand this way of being because I was also a "disaster thinker." Always worried and wondering what next? (The "next" wasn't something pleasant, either!) I'm thankful that I have tools and techniques in place that have allowed me to recognize and transform those thoughts and emotions when they do arrive - far less frequently, I am thrilled to report!
Life is much more fun when I get to be the welcoming queen of my castle!