No, this is one of the worst things about mental health problems, they're not always easy to see from the outside if at all.
My dad suffered with depression for years and still does. I didn't know until recently, I always took him as he was. It can break a person down and it's easy from the viewpoint of somebody without depression (such as myself) to say "oh come on cheer up" but it really isn't that simple. It's a horrible horrible thing.