When you began to reminisce, brain cells dormant just seconds before began firing chemicals at one another. That action triggered regions of your brain involved in processing emotions, which is why you may have re-experienced some feelings you did at the time of the event. Chemical and electrical signals shot out to the rest of your body. If you were stressed before you began this exercise, your heart rate probably slowed and stabilized as levels of cortisol and other stress hormones decreased in your blood.
I remember the eureka moment I had about procrastination when I was still a high school Latin teacher. There was a lot of talk about "time management" and "SMART" goals going around the faculty in-service day training. But then one of the teachers spoke out, "This isn't time management as much as it's about an emotion they'd rather avoid." At the time, I volunteered to be a practice client in a coaching session,