As leading scientists warn that society has become "supremely arrogant" by ignoring the importance of sleep and the body clock, we examine the profound impact our internal clocks have on our body.
Explore the eight body clock phases and take the quiz to see if you are a morning-type "lark" - or an evening "owl".
Authors: James Gallagher, Rachael Buchanan and Victoria Gill
Produced by: Andreia Carqueija, Richard Bangay, Marcelo Zanni, Helene Sears and Dominic Bailey
With thanks to researchers at The University of Oxford, The University of Manchester, The University of Surrey, The University of Cambridge and Harvard Medical School.