Why do we need sleep? What does it do for your body and mind biologically speaking? Is it necessary? Can you die from lack of sleep? Also why do different people work on different amounts. For example, I sleep about 3-4 hours a night. Every couple of weeks I might sleep for 10 and then I'm good on 3-4 again for a while. But I know people that can't function unless they have 10 hours every night. Does anyone know what could cause this?