Every couples therapist knows the experience. Just moments ago, as you talked to the wife and then her husband, you were struck by how likable each one seemed. You sensed their warmth, their humor.

But now you've hit on one of those issues—perhaps it's a conflict about an in-law, or something about sex, or even the proverbial struggle about the toothpaste tube—and suddenly the people whose company you were enjoying earlier appear to have left the room. Faces tighten bodies grow stiff nobody's hearing anything any more. Now two unyielding go-for-the-jugular combatants are sitting in front of you. And they're not the only ones who have undergone a dramatic transformation. Suddenly, you're not quite present in the room either. As garbled little voices in your head issue their fuzzy instructions the couple before you begins to fade. You tell yourself you must do something. Meanwhile you note with some distress, a decidedly unprofessional feeling of panic has begun rising within you.

Of course, one needn't sit in a room with warring couples in order to find evidence that we all regularly experience rather dramatic shifts in our moment-to-moment sense of ourselves. We all know what it's like to experience a seemingly trivial incident as a life-or-death struggle and then, later, looking back over the experience, find ourselves totally unable to understand what the sense of peril was about. It is as if some other person was feeling the anxiety—a…