Sleep is very important for every mammal, reptile, bird, and amphibian. Bat needs 20 hours of sleep per day, human eight hours and giraffes two hours. The animals that are low in food chain sleep less and this protect them from predators when they sleep in dark safe place. But these theories hold conflict. Why human sleep? As they have no fear of predators. Different people have different opinions about why they sleep.
Some people say that our body needs energy to work and we get that energy from food. When the food in our body does not generate energy then we feel sleepy and body wants to stop for a while. Another theory is that during the sleep the energy of our body is used to repair the nervous system, immune system, muscles and bones of our body. Experiments have proved that if a person is deprived of sleep then it affects his memory, speech, language and skills to handle a problem. May be the one function of sleep is brain development. If a person is awake for 17 hours it will be equal to the blood alcohol level of 0.05%.
One of the experiments has shown that dreams during sleep stores the important memories and diminishes the unimportant one. It helps to maintain the data in our brain.
There are three glands in our brain that controls the sleep system. One is the â€œinternal clockâ€. If you sleep at a particular time for many days then this gland stores this information of time. And the second is linked with your eyes. When eyes see darkness it makes the third gland produce a hormone which relaxes your body and makes you feel sleepy. If you remain in a place where no natural light reaches then your brain will let you know that it is the time to sleep at nearly the same time.