Probably around a decade ago I was diagnosed with a slew of things and put on, among other drugs, SSRI's. I never felt depressed at time. Interestingly, I felt angry, powerless, etc. but not depressed. The drugs really didn't feel like they had any effect on my mental state or behavior.
Then maybe around 2017-2018, after living mostly in isolation (outside routine requirements like work, etc.), things started to go downhill. I spiraled into a period of what I'm sure is depression. Since, then? I might be able to crawl out of it every now and then (around mid-late 2019-2020 I had some sort of strong resolve come over me that lasted a few months) but ultimately just return a depressed, monotonous and sedentary state. I'm generally good enough and keeping together in public, but in my private life it's on full display display. The pandemic did good work to undo everything I had tried to fight it, but the isolation isn't anything new and I'd likely have returned to it in my own eventually.