We spend a third of our lives sleeping, but researchers are still not sure why the body needs so much sleep! In fact, researchers regard sleep as one of the greatest unsolved mysteries of science. Some scientists believe that sleeping helps the brain rejuvenate itself, thereby helping it pass on the right directions to other organs of the body once the person wakes up. When a person sleeps, the vital organs work at a slower pace. During this time the body heals itself, the mind rests and the organs recuperate. Lack of sleep results in irritability and moodiness. It also slows down speech, flattens emotional responses and reduces the ability to memorise and multitask. Sleep is thus essential for a person's health and wellbeing.