I too am a trained actress-trained in NYU's Grad Acting Program by some of the best teachers around. I would agree with H.R. It isn't a matter of emotional regulation, but a redirection of the emotion. Often when one is most upset or out of sorts,the best acting can occur. The energy that the actor may be feeling in real life is redirected into the action of the character. I was taught (and teach) that emotion is a result of pursuing an action (or objective, intention, etc.). One pursues the goal completely (even though one knows the goal may be unattainable) and encounters obstacles. This is where the "emotional" response occurs. Just as it does when one is playing a game to win. It isn't "real", yet we fight hard, and become frustrated, angry, sad, when we can't achieve a win. And we are happy, excited, etc. when we make strides in the direction of winning. In one exercise I do with my students, a group of individuals is charged with making a perfect circle out of a group of chairs. A second group is charged with setting the same chairs in a perfect line (at the same time). The range of emotions the students feel as they try to achieve their goals and are frustrated is a great example of how emotion is a by product of action (at least in acting terms).

So, understanding what the character wants and why, and fighting for that with complete commitment, is where the emotional response is created (at least for an actor). I don't have a degree in psychology, so maybe there is a scientific or psychological explanation (maybe this is indeed the concept of emotional regulation-but that sounds much too controlling to me)