It is already well known that imagining certain things can have a physiological effect on us. For example, imagining an intense situation can cause the heart rate to go up, while imagining a quiet, safe place might have the opposite effect (or maybe that one is simply a result of distracting oneself from whatever may cause unrest).
Another example would be imagining yourself doing something you don't want to do. From what I understand, this reduces the stress of anticipating work.
I wonder, though, what exactly separates this from actually doing what you imagine? what are the differences in the physiological effects? How different is the activation of the brain? (aside from the obvious - for example, imagining something physical happening to you, such as being punched, won't actually cause any bruising)