 Nobody ever says, it's just cancer, get over it. Or snap out of it, it's just diabetes. And who would ever say, it's nothing serious, it's just heart disease. But you do hear those words about people living with another serious illness. It's called depression, and it threatens the lives of more than 15 million Americans. Like heart disease, its symptoms can be misleading. Like diabetes, it's biologically based. And like cancer, it can be fatal.