A whopping 63 percent of Americans report not getting enough sleep during the week, according to the 2011 Sleep in America poll from the National Sleep Foundation. While it’s generally recommended that adults log seven to nine hours of sleep, not everybody fits this rule, says psychiatrist Tracey I. Marks, M.D., author of Master Your Sleep. Some people need more, others less (but no fewer than six hours or you’ll become chronically sleep deprived). How do you know the magic number of hours you should snooze? Let your body be your guide. Go to bed when you’re sleepy and wake up without an alarm clock.