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Thanks so much for sharing your experience and some detailed relevant facts! I will go have a think about this. Comments like this are definitely making me think.
I come from an upper-middle class family, both parents still married and happy after over 25 years, always had a roof over my head, food in my stomach, and an excess of material items beyond my needs. I have no severe traumas, never had a TBI, never been abused, and so forth. By all definitions, I should be happy without any issues, and I usually am.
My father struggles with depression. We both can understand what it’s like to feel like a literal cloud rolls in from beyond the horizon and over our heads, and like a light switch, something in our brain makes a change and it starts to rain. We are both diagnosed with major depressive disorder, so is my paternal grandfather. We all three take the same antidepressant, Wellbutrin, and have for years. The brother of my 3rd great-grandmother (so my 3rd great-uncle) shot himself in the head and killed himself when he was in his early-30s, back in the late 1800s. Depression runs in my family, there’s no question.
Both my dad and I have a mutation in our SLC6A4 gene, which is responsible for producing serotonin receptors in the brain, that causes us to produce less receptors than the average person. There are several studies that suggest a connection between this mutation and depressive disorders and OCD. The link is still not certain, though. Nonetheless I think it’s an important thing to mention. There is ongoing research to understand how genetics play into depression.
My biggest trigger for a depressive episode is stress. When I experience enough of it in a certain period of time, my brain’s response is to essentially shut down. Look up the diathesis-stress model. It theorizes that psychological disorders are a result of the interaction between predispositional vulnerabilities (genetics, trauma, etc.) and stress from life experiences. This is why while my brother or even someone unrelated to me won’t develop depression in response to X amount of stress, others like myself will.
This is a biological thing, it is real and it is observable. Depression is an incredibly complex and multi-faceted issue, and it’s not always purely genetic. But as you can see for me, I have at least two direct, and one distant relative, that experiences/experienced depression.