One of biology biggest mysteries is why do we sleep. In spite of decades of research. Scientists still haven't figured out the secret of sleep. If you are aware of the arguments and research. You would know that anabolism can occur even while being still... so why do living things have to spend one third of their lives sleeping? There are no animals that don't sleep. Even whales that continously swim have to alternatively make their left and right brain sleep at a time. It is also observed that the smaller the animal is the more it sleeps.. this is why rats sleeps 14 hours a day versus human 8 hours and elephants only sleep 3 hours. Maybe there is a clue here somewhere? Why is resting by being still not sufficient? One can't reason the brain is being rested while sleep because it uses even more ATP when sleeping such as during REM sleep. Is it about memory consolidation? But it could just be a secondary to the real purpose of sleep. If you have heard of latest cutting edge research about the purpose of sleep. Do share it.