I am an (at least) third-generation depressed person through my maternal line. In fact, when I finally worked up the nerve to go to my family doctor for treatment on this issue a few years ago, I barely got three sentences out before he started nodding and saying "Yup, I know your mom."
My mother's depression has curdled my relationship with her and my ability to perceive her as a person. Rationally, I know she needs better support in the form of consistent talk therapy and medication, and I know I (of all people) should be sympathetic to how she feels when she's not in treatment. But realistically, I can barely tolerate being around her most of the time.
I have known I suffered from depression, to some degree, since I was twelve years old, but I did not receive treatment until I was 24. As a teenager, I asked my mother if I could see a therapist, but struggled to voice the problem to her, and that help never materialized. As a college student, I struggled with eating disorders and spent weeks in bed, but managed to do enough work to get by with decent grades, and nobody really realized how deep I was in it. Finally as a young adult in a job at a school, I talked to one of the school counselors about how I thought maybe I was depressed. Her first question was, "Does it manifest as sadness or as irritability?"
It was like a lightbulb. Although I had read on the subject, it hadn't come up that irritability was a symptom of depression. Personally for me, my depression doesn't manifest that way, but I realized in that moment that my mother's has long done so. It's interesting to understand her in this fashion. But it doesn't make me feel better about her or about my relationship with her.
At 24 I started taking anti-depressants and going to talk therapy with a licensed professional counselor, who I have continued to see, off and on, for the past five years (I'm 29). The talk therapy has had mixed results; it saved me once when I was going through a difficult period professionally and personally, but when in non-crisis mode, I'm not sure how much it really helps me. The medication, on the other hand, has been life-changing.
My depression tends to manifest as apathy more than anything else. When I get overconfident and stop taking my medication, I find myself unable to care about getting out of bed, cleaning my house, washing my clothes, paying my bills, doing the ordinary, necessary steps that life requires. I am lucky that it has never progressed to be so bad that I couldn't go to work or take care of myself at a basic level, but I can see how that could happen if I weren't careful. Medication doesn't change me fundamentally, but it allows me to motivate myself to take better care of myself and to be more proactive in my personal and work life.
If I could go back in time and change anything I would make sure I got attention for this disorder and treatment at an early age. It really hurts me to think about myself at 12 years old and having suicidal ideations. I was just a child. There are children I work with who are the same age and have had similar problems, and I do everything I can to help their families find the resources they need. At the time I was so secretive I don't know how my parents could have known about it, but I also resent that they didn't. I am also still upset by the fact that when I reached out for help, nothing was done.
Honestly it makes me think that, when/if I have kids, I would like for them to see a mental health professional at least once a year or so, just to have a "checkup" in the same way that you would have a child see a physician regularly. Parents don't always see the symptoms, and to be fair, a lot of the time, children work very hard to hide their depression and other mental illnesses when they can.
One more thing I want to talk about, when thinking about depression I have to think about the "friends" that come along with it. I don't really know any other depressed people who don't struggle with other issues. Personally my co-morbidities have been generalized anxiety disorder, nicotine addiction, and eating disorders. I'm not an expert on the subject so I can't really say which is the chicken and which is the egg. But it's a complex topic. Someone like me has a very different kind of depression than someone who struggles with ADHD and narcotics, for example. It makes me feel frustrated to hear other people talk about mental illness and say things like "well, I recovered without resorting to xyz treatment, so other people should, too," because not everyone's depression is the same. Kind of like how there are all different kinds of cancer.