Here I list some purposes to consider some world situation other than what you believe to be the case. To wit: Many parts of the brain will be required to contemplate these hypothetical situations, while sill holding to the fact that they are merely hypothetical. This seems to me to be a well solved, yet difficult, engineering problem. There is some mechanism to suppress real muscles upon dream state visions of vigorous motion. This mechanism fails sometimes. It is sort of like the hypothetical suppressor above, but different I think. Children are good at distinguishing the real and hypothetical.