OMG Myzen, I'm in the freaking HOSPITAL trying to find an answer to this question -- not to mention working on it quite a bit with my regular therapist.
In fact, my inpatient pdoc and I talked about this just today.

My dad drank and my mother has untreated BPD and depression. HER father hanged himself when she was in her early 20s (well before I was born). Sad to say, the crap runs in the family.

There are a couple of things I've realized about this particular question, at least for myself:

1) Since nobody can see it, it must not be real. This is at least how most people treat me, especially at work. "Well, you don't LOOK sick." Or, as I was told someone said last time I was inpatient, "Oh, she's not depressed. I've heard her laughing."

2) I'm not ready to blame the people who helped make me this way. Some of it is genetic, and some of it is very real abuse that, they tell me, no one deserves. I'm still working on that one for myself.

Also, I think there's this thing with the stigma. Who the hell wants to admit to being "mentally ill"? I think of "mentally ill" as schizos and worse. Me, I'm just depressed, anxious and traumatized. As far as I'm concerned, you can get that way from daily living, LOL. So I don't see it really as an illness, it's just the way I am.

My first episode of depression was at age 14. I found a checklist of depression symptoms in a newspaper article and read them to my mother and told her I had every one of them. She blew it off as "teenage angst" and I got zero help. I tried counseling in college and had a terrible experience, so didn't go back for 10 years. The first therapist I had when I tried it again lasted 2 months before having a quintuple bypass and having to retire. So I tried to live with it a few more months, and when it became clear that it was either get help or die, I got help, and here I am, 6 years later .... still a mess.

Whew, kind of went off on a tangent there, sorry. Just know you're not alone.

Candy