By Vidya Rajan, Columnist, The Times The death-like appearance of sleepers has fascinated people for millennia; death is even euphemistically called “eternal sleep”. But why do we and other animals need sleep? A good night’s sleep is considered a key to a clear head, and most of us sleep between 6 and 8 hours. But some notoriously high achievers, including Leonardo da Vinci Nikola Tesla,...