Everyone thinks they're immune to anxiety until it gets them. I used to even be able to handle a major trauma here and there without breaking a sweat. Then I got hit with two extreme traumas back to back, and since then, my resistance to daily traumas is gone. What I find funny is that from an outside perspective, I might even seem more resilient.
When I see people who have the same attitude I had before the trauma, I worry. It's like seeing a kid on a highwire. Oh, baby, I know it looks so easy, and everytime you've tripped you've caught yourself. But you don't know how far down it is.
I've written a lot about social collapse, but now I'm thinking about something like identity collapse. You develop a personality, a set of habits, that gets you through life, and it's probably more than half subconscious, learned when you were very young, and hard to change. But then some key component changes -- it could be something in you, or something in the world, or your role in the world. And gradually, or suddenly, your whole way of being no longer works.
When this happens to a society, or to an individual, and they don't flame out in destruction but fall into a deep slump, we use the same word: depression. The whole system becomes disjointed and ineffective, and recovery is a long process of rebuilding a working system from scratch.
I'm thinking about people who are blind from birth, and then their eyes get fixed. You'd think they'd be happy, but normally they become depressed, because they still can't see. It takes years to learn to interpret the light on the retina as a three dimensional world, and they have to learn this as an adult, where normal people learned it as babies with highly flexible brains. Meanwhile, now that they've become aware of that maddening world, they can't ignore it.