By Pierre el Khazen, All of us spend some time sleeping and we know its necessity. When we sleep, we are not conscious and not able to know what goes around us. When we sleep, we go through physiological changes called physiological correlates of sleep which act according to what we experience when sleeping. There are different levels of sleep such level 4 sleep where people are relaxed, deeply asleep, and find it hard to wake up. In level 2 sleep, people are a little asleep and could be easily awaken up. They are 4 levels of brain activities that we move from one to another through our sleeping at night. When sleeping at night, we experience 5 to 6 cycles of sleep. A typical night of 7 – 8 hours will let us go through 5 – 6 cycles of sleep where the first cycle of sleep would reach level 4 while the others would decrease levels in each next cycle of sleep. Pls Click "READ MORE" to view the whole article.