The problem is when one reacts automatically in a given situation. Without consciously planning it or deciding it, one just immediately feels a certain way, or one just acts in a certain way. That is fine if what you do is working. If it isn't working we might start talking about unwanted reactions.
Usually a reaction is based on information or learning gathered somewhere else or sometime else than the present situation. That is, one arrived at that way of reacting based on one or many events that happened years ago. Or, one perceives the situation as being something else than it is and one reacts based on a totally different real or imagined situation.
At any rate, if the reaction you have is inappropriate or unpleasant, it is probably in need of being cleared. We can clear up what the reaction really is about, we can find the proper context for it, and we can establish a more clear way of responding that fits the present situation better.
If your stomach cramps up whenever you are about to say something to your boss -- that might not be a very useful reaction. It would be a likely target for clearing. That means, we would process that feeling, discover something more about it, why it is there, what it is about. We would finish what is unfinished, and we would add in missing resources. In the process of doing that, the unwanted feeling would probably vanish, or at least diminish. That is not so much because we are getting rid of it, as it is that we put it back in its proper context while finding out what it is about. We bring some clarity into the whole thing, and after that one can have more clear, useful responses.