I've definitely noticed that I get more creative as I lose sleep (seeing as I've got plenty of opportunities for that to happen, having chronic insomnia). The only problem is, at the same time I tend to become even more ADD and unable to focus.
Reading the book Left in the Dark, it suddenly made a lot more sense why this might be. Basically the left brain is used predominantly throughout the day, and is dominant, suppressing a lot of the right brain's function, but it gets tired first, eventually ending up in a state a lot like sleep if we don't actually go to sleep when it's ready, but we are still awake as the right brain is then able take over, as it is no longer being suppressed to the same degree. It is the right brain that handles our more intuitive, artistic capabilities, while the left handles language and logical reasoning. It's possible that dreams may be the right brain giving itself something to do while we sleep, as that's normally the only time it's not being suppressed by the left, unless we are getting sleep deprived.
There's a website for the book at http://leftinthedark.org.uk/, and checking it just now I've noticed that a lot of the book's ideas, supporting evidence and the latest advances to the idea are now on a website at http://beyond-belief.org.uk/.
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You aren't thinking or really existing unless you're willing to risk even your own sanity in the judgment of your existence.