Just push a button, think a happy thought, take a pill, whatever, drift off into lala land for a few minutes, and end up feeling as refreshed as if you've just had a full night's sleep. Ok, so there's about 50 million holes in that little theory, not the least of which is the fact that I'm fairly sure I just made it up now. But, actually, it would explain quite a bit. Such as how you can nap for 2 hours, have very vidid dreams, and wake up feeling refreshed, whereas you can get 10 hours of fitful, dreamless sleep and wake up feeling more tired than when you started. Lots of other important stuff does seem to happen while we sleep, though, such as fighting infections and producing healthy blood cells.
More questions arise, though.
To my knowledge, no studies have been done on this. For all we know, REM may be what drives our white blood cells to drive off infection while we sleep, and it may be what promotes the growth of healthy new cells. Of course, it also might not be. Just seems like a neat idea, that's all. In my perfect little world, sleep would be optional, but people would still do it if they had the time, because, even if we discover the brain chemical which will simulate the good feeling we get by sleeping, there's no arguing with the fact that sleeping will always feel good.