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. Get all the info you need here.
Super Serenity Sleepers
The Guide To Sleeping Productively