For the purposes of this discussion, “reactivity” means reacting to external stimulus in ways that cause undue stress. When you are verbally assaulted, for example, you can respond instinctively, both physically and mentally. You may get annoyed as you arrive at work and see that you have extra work on your plate, and you may say or do something you later regret.
When your partner promises to wash the dishes then you return home to find the kitchen in disarray, you can become enraged, isolate yourself, or attempt to make your partner feel bad. You might feel as though you don't have any power of your behavior.
You're acting instinctively—reactively. Another choice is to practice mindfulness. Often in the middle of a stressful situation, exercising present-time mindfulness allows you to become conscious of your urges (reactive patterns), pause, maybe take a breath, and respond skillfully in a manner that does not cause any harm. As one meditation student found, with some insight into oneself, wise deeds are sure to follow.
Gino, a twenty-eight-year-old college student, was late when he drove on an L.A. interstate, and he missed his exit when someone cut him off. An outburst of anger swept through his body almost instantly. He may have made an irritated hand gesture or screamed ineffectually at the long-disappeared car in the past. He would have stewed in his anger, his blood pressure rising, and he would have become consumed with retaliating against the other driver. He wanted to use this moment as a way to become conscious of his reactivity and make a new decision while he was practicing mindfulness.
Wow, I'm very mad, he thought as he took a breath and felt his body—heart pounding, sweat in his chest, clenching in his stomach. He was finally able to joke about it after reading about whether a little thing had caused such huge indignation. His body started to relax as he became aware of this. He realized at that moment that he might react differently in the situation. He found he was still furious, but not as exhausted as before. He also considered letting the pickup driver into his path. He was able to make the decision because he was conscious.
You may also want to read more about Mindfulness Meditation and Healing here.