Depression is an illness in the same way that diabetes or heart disease are illnesses. Depression is an illness that affects the entire body, not just the mind. Depression is an illness that one in five people will suffer during their lifetime.
Depression is the leading cause of alcoholism, drug abuse, and other addictions.
Untreated depression is the number one cause of suicide. Not a character flaw or the sign of a weak personality. Unfortunately, doctors find it extremely hard to diagnose depression. If you are not feeling good, and it doesn't go away - tell someone. Your teacher, counselor, doctor, friend, anyone.