Depression--What You Need To Know (TeensHealth)
It's normal to feel moody or sad at times. But with depression, a sad or bad mood lasts for weeks, months, or even longer.
Depression affects more than a person's mood. It can affect the way they act, and how well they do in school. It also can affect their energy, sleep, and eating. Depression can even contribute to physical symptoms, like headaches and stomachaches. If people are depressed, they find it hard to enjoy things like before.