In some ways, happiness can be just taking a little thing and making a big deal about it. The "big deal" can be either an outward or inward expression depending on your personality type and depending on the "little thing" itself. The little thing can be any thing that gives you joy and occupies your mind. For me, the little thing can be whatever hobbies I'm interesting in at a particular time. The strange thing is that every rare once in a while (like the other day) it all seems so pointless. What does it matter if I do that hobby? No one cares about it and it does not really do anyone any good, except that I am happy when I do it, but for this one day. The next day, the feeling is gone and I'm happy again, and I don't even need the hobby to be happy that day. It's just "all good" again.
Now I ask myself, what if this "empty" feeling hit me every day? I think I would be depressed and life would seem utterly pointless. This is the closest I can get to understanding what a depressed person must feel, and I know it is still infinitely far away from the real feeling itself.
I get an occasional bad day of anxiety too, and then brush it aside if there is no action I can take to minimize the chance of disasters. But again, what if it happened every day?
You have to do whatever it takes to get that brain chemistry back on track. For some people it is automatic. The feedback loop corrects for the disturbance (big ones and small ones) that knocks you "out of whack". For other people, it takes more effort, but they can do it without medicine. For others, medicine is the answer. Kitty Dukakis advocates for electroshock treatment as that is the only thing that works for her.
Back in the 1970s my mother would suffer for years with depression, once the depression was triggered by a tragedy, or even something much less than a tragedy. She would never bounce back until the depression made her angry (at God? the world? herself?, who knows). It could take 6 months to 1 year to get angry enough to recover because she is not someone who easily gets angry. Nowadays, she can use medicine, and she need not suffer more than a few weeks. Hence, instead of the majority or her life being "torture", a very tiny portion of her life is like that now. And this, even after my sister died of cancer. She is sad about it for sure, but not depressed and there is a very big difference between the two states of mind. Tragedy and sadness, as well as triumph and elation, are normal parts of life, but depression is not a necessary evil, even if periods of sadness are.
I'm an engineer, and by chance, one of my areas of study is "control theory" where we study feedback systems, stability, instability, control and lack thereof. Just like the body, the brain is a machine, and just as not all our bodies are equally coordinated, neither are our brains. And that is not to say, that such "less coordinated" brains are defective, because often such minds are also very creative and intelligent. If you wished all the "depressed people" away, you might not have much of a civilization left, or maybe one you would not want to live in.
... OK, end of babbling. I think there was a point somewhere in there.