The average adult needs 7 to 8 hours of sleep per night. Teens need about 9. When you get less sleep than you need, your body does not just "adapt," but rather you may begin to experience symptoms of sleep deprivation. Your judgment and reaction time may slow, you may experience memory loss, depression, a weakened immune system, and pain. It can be especially dangerous to drive when you're sleep deprived since focusing and keeping your eyes open can become difficult. Follow the links below to find WebMD's comprehensive coverage about how sleep deprivation affects your body, how much sleep you need, how to get more sleep, and much more.