I believe that there are two kinds of depression: real, and fake.
The first kind—real depression—is very real. And for that, please seek help from a doctor.
The second kind is awful too, because it is preventable. It's usually just a result of us drifting off the path of habits that keep our brains happy.
This my flowchart whenever I am feeling off. These are the questions that I ask myself, and quite often I don't get past the first two questions before I see why I might be feeling down.
Click here for a larger image.