Sleep is part of a person’s daily activity cycle. There are several different stages of sleep, and they too (36) in cycles. If you are an (37) sleeper, your sleep cycle is as follows. When you first fall into slumber (安睡), your eyes will (38) about a bit, your temperature will drop (39) , your muscles will relax, and your breathing is slow and becomes quite (40) . Your brain waves slow down a bit too. This is called stage one sleep. For the next half hour or se, as you relax more and more, you will (41) down through stage two and stage three sleep. The lower your stage of sleep, the slower your brain waves will be. Then about 40 to 60 minutes after you lose (42) you will have reached the (43) sleep of all. This is stage four sleep. (44) but instead about 80 minutes after you fall into slumber, your brain activity level will increase again slightly. (45) This period of rapid eye movement lasts for some 8 to 15 minutes and is called REM sleep. It is during REM sleep period that (46)