There have been tons of studies on sleep and how much you need is pretty well understood: - Most people need ~8 hrs of sleep a day. - Any less than what your body needs and you'll be cognitively impaired from sleep deprivation. - Sleep deprivation will cause health problems and early death. - 20 minute naps will give you a boost but never get you fully rested since you don't go into deep or REM sleep (for which you need a full ~90 minute sleep cycle). - High levels of caffeine intake will disrupt sleep in most people, leading to sleep deprivation.