What is the main idea of the passage?

Sleep is not just a time for the body to rest. Scientists have found that the brain stays busy at night, organizing the information we learned during the day. In one study, students who slept for eight hours after studying remembered more new words than students who stayed awake all night. Sleep also affects mood and concentration. Teenagers who regularly sleep less than seven hours a night are more likely to feel irritable and find it hard to focus in class. Experts recommend going to bed at the same time every night and avoiding phone screens for an hour before bedtime, because the light from screens can make it harder to fall asleep. What is the main idea of the passage?