All day long our brain is designed to play, and re-play our life experience and saved inputs concerning our beliefs, and perceptions to us. I like to call it the stories we tell ourselves. They are loops of thoughts that we can get carried away with if they are negative. Usually we do not have this issue with positive experiences. Some people recognize when this process begins to happen to them by likening it to "spiraling or spinning out of control" because the thoughts begin to rush in and pull us in a negative direction. The trouble with negative thoughts is they begin to affect us physically also.