It's seriously an altered state.
Most of the time I'm not in that state[1], though. In those cases, I don't think I really visualize anything. I think my mind is too occupied with egg-juggling to have the cycles to spare on visualizing things.
[1] The older I get, the more difficult the state is to achieve and the more delicate it is when I've achieved it. Which is a shame because my best work is done in that state.