I am replying to this many years later so I am unsure if you will read this but here are my thoughts about your question. According to neuroscience, the old belief that humans only use 10 percent of their brains is incorrect. Much of our brains remain active even during sleep.
However, there is a difference between what our conscious mind will process versus our subconscious minds. Our conscious mind deals with what is here in our physical dimension. The subconscious mind is not and therefore is unrestrained by such limitations.
When we sleep, our conscious mind sleeps, allowing our subconscious minds to reign. That is why what seems impossible is possible in our dream scenes.
It is fascinating!