Hi, People sleep at the equivalent of one-third of their lifespan. About eight hours of sleep per night ads up to nearly three thousand hours per year. Calculating from an average life expectancy of seventy years, this adds up to about twenty-four years of sleep. The essential aspect, however, is the rhythmic alternation between waking and sleeping; everyday begins a new with approximately eight hours work, eight hours for our selves, for free time activities and family, and eight hours of sleep. Marvin.