Are all of the animals sleeping?

Sleep is probably a very ordinary activities that we are doing every day, but the scientists are headache to solve the mysteries of this normal operation. No exact reason why we need to sleep and slept much, a normal person spends about 1/3 of our lives sleeping.
Not only sleep studies in humans, the scientists also studied the sleep of many different species and discover more interesting things. The animals do not have to sleep the same, there are species lie down to sleep, hanging upside down on tree species to sleep, standing to sleep. There are even species undergo a very long sleep to survive the winter, that we still call a hibernating species.
There are a lot of animals like bats, they sleep an average of 20 hours per day and only operate at night. Meanwhile, giraffes sleep only 30 minutes per day. And most mammalian species more sleep in the immature stage.
The sleep of the animals still hides many mysteries than humans, some species can alter normal sleeping form in the different conditions. As some migratory birds may sleep less, or even don't sleep when finding a new place. Some other animals also sleep unihemispheric, a form very special sleeping when only half of the brain to rest completely, while the other half remains normal activities such as whales and dolphins.
While higher-order animals should sleep, the lower organisms have no clear concept of sleep because their brain simply does not need to rest, in this species only the declining activity physically as a rest of the body. Using methods of measurement function in fruit flies, they recorded the amount of time they rest by reducing the operational functions of the body. In an interesting experiment they found that the flies are not reflective of rest will be much slower in the search for food.
Fish is one of the creatures not much research about sleep, by the difficult conditions of the study. Scientists believe that some fish species often operate in groups will swim continuously without sleep, while some other fish species alone activity can still sleep at night. But sleep was short and species vulnerable to disruption due to the surrounding environment in the water. Some fish during spawning migration activities also leaves their sleeping habits.
Reptiles are one of the species "dead asleep". Scientists discovered patterns in the brain waves during sleep reptiles are different from mammals, the brain wave activity of them reduced to the maximum. When was sinking into a deep sleep, it is difficult to wake them up, especially the large reptiles like crocodiles, komodo dragon.

Refer:  HowStuffWork, Wiki