I've just come up with this, so it's a bit of an underdeveloped theory (read: completely bonkers), but it does sounds at least a tiny bit plausible.
Let's look at consciousness as a value on a scale. The marker on the scale varies between purely internal and purely external. Either extreme would be a dangerous place; purely internal, and you're basically in a coma, while purely external would mean a drone with no imagination. I would submit, however, that the brain/mind goes between those two extremes quite often. I would even say that sleep is near the internal extreme. After all, we dream, yet external stimuli can still wake us.
I would even say that certain neurological disorders, such as schizophrenia, would be caused by having your balance be in the wrong place. People with well developed imaginations are simply able to move back and forth between internal and external life, allowing their imaginations (internal) to try new things rather than doing it in the real world.
Where am I going with this? No clue. But if I can develop it further, and if it does actually explain things, then it could be both useful and fun.