I would often do this for job interviews..during natural vivid visualization of the interview..and this would typically lead to a very good performance. However..I am a confident @ss anyhow..and tend to perform and focus well in interviews and tests.
However, if it is an important job task that doesn't interest me that is also time sensitive..watch out! The more I tried to focus the more frustrated, distracted (and mentally tired) I would become. I would often procrastinate doing unrelated side tasks, surfing the web..etc..until I had wasted away a vast amount of time..sometimes a day or multiple days.
I think we need to contact WEbsters - headversations is the perfect word for it! I do it so much that sometimes I forget that I haven't actually had the conversation! I think I'v etold somebody something and then when they don't know what I'm talking about, I realize it was only that I had mentally told them - too bad more people aren't psychic (or maybe it's a good thing people can't read my mind!). I do this alot too much, reherse convo's b4 having them, either for fun or cus its important, in a day dreamy manner.