Sleep is defined as a state when the motor activity and senses are suspended; there is partial or total unconsciousness, and the voluntary muscles of the body are not active. It is more reversible than coma or hibernation, yet responds less to any kind of stimulus than silent wakefulness. Sleep is very important, as it is the rest cycle of the body. Doctors say that this cycle is a heightened anabolic state - a certain period when the body produces new nervous and muscular tissue and bone. To put it simply, this is a period when the body grows and being repaired. Sleep is triggered by a group of hormones in the body. These hormones react to cues within the body and in the environment.