Young adults are notorious for not getting enough sleep, with most averaging only six hours a night. Young adults need an average of 7.5 and 8 hours of sleep every night (you may need slightly more or less).
As you move from adolescence to young adulthood, sleep patterns change. Sleep often becomes less satisfying: you might not sleep as well and feel less rested in the morning. To understand why, take a look at the sleep cycle.