Have you noticed that each time you replay a past negative experience in your head, your body reacts to it also?
When we haven't yet healed from a past insult or other unpleasant experience, including ones that happened many years ago, we're carrying that experience in our emotional body and in our physical body.
You can test this easily. When you're aware that you're replaying a disagreement or something else that upset you, notice what your body is doing. Is part of it tense, heavy? Notice where in your body you're reacting. Note how it feels. What's the difference between before and after the negative thought?
Can you see that replaying negativity is continuing to harm you? Some things are more difficult to heal than others, but do you see how important it is to do the inner work surrounding that issue? Stress plays a huge role in creating illness.
If you continue to react to something over and over, there are many questions to ask yourself so you can identify the original source of your reaction. You owe it to yourself to investigate.