Going to sleep may seem pretty boring compared with all the fun things you do while you are awake. But there's a lot going on in your mind and body while you are sleeping. Sleep, in fact, is as important to your survival as eating and drinking. Sleep improves your mood, makes you a better athlete, and helps you remember and understand what you learned during the day. During sleep your temperature drops. Your heart rate slows. Down goes the pressure of the blood moving through your veins. A chemical that controls growth (called a hormone) moves into your bloodstream. Scientists think that sleep brings back energy and improves your immune  system. We know what happens while we're asleep because scientists study volunteers who sleep in laboratories. The sleepers are connected with machines that measure brain waves, eye movements and muscle activities. Sleep is like a school day: it's divided into different periods, or stages. When you are awake, your brain waves fire rapidly. As you begin to relax and drift into the first stage of sleep, your brain produces slower-moving waves and you lose awareness of your surroundings. As you slide to deeper sleep, your body repairs itself from the normal wear and tear of daily life. Then, as you begin to drift back up to a lighter sleep, your mind becomes more alert, and your dreams begin. You are in REM sleep. REM is the name for the rapid eye movement that happens while you are dreaming. During REM sleep, your eyes move back and forth behind your lids , as though you were watching a movie. During other stages, you might move in bed, but during REM sleep you're still. That's probably because if you could move, your body would act out your dreams. As you get close to morning, you spend more time in REM than in deep sleep, so you dream more. Researchers know that during REM sleep the part of the brain that handles learning and thinking is very active. Getting too little sleep can affect your personality. Experts recommend that children get at least nine hours sleep a night. Sleep has many advantages except   _  .
improving your mood making you strong helping you study practising your eyes