The opposite of control is acceptance. ACT can help to increase your acceptance of anxious feelings and thoughts through interventions that develop your awareness of two aspects of your experience:
When we experience strong emotions, there is a tendency to respond as though we are our emotions. This is even reflected in our language when we say things like "I am anxious." The truth is, even at its strongest, anxiety is just one aspect of your experience. As such, it is something separate from the "You" that is experiencing it. You are not anxiety any more than you are the screen of this computer. The anxiety, the computer, and the words on the screen are all parts of your experience. As the experiencer, you are "bigger" than your experience. ACT therapists use mindfulness training as well as other techniques to help you to move toward perceiving anxiety as just another aspect of your experience.
When we are very anxious, instead of recognizing or identifying our anxious thoughts as what they are (just thoughts), we experience them in the same way that we would experience the real-life events that the thoughts refer to. When this happens, the thoughts are said to be "fused" with their referents.
For example, a husband who has a disagreement with his wife might have the thought "what if she divorces me?" While this is only a thought, and refers to events that may in fact be unlikely, the husband might feel many of the same emotions he would experience if he were in fact going through a divorce. Similarly, the person who is having a panic attack might have the thought "I am going to die", and experience as much anxiety in response to that thought as they would if their life were actually threatened.
An essential part of accepting our thoughts is recognizing that they are separate from the events to which they refer. In ACT, this process is called "cognitive defusion." ACT therapists use a number of interventions and exercises to help their clients experience thoughts in a "defused" way.