It's that 'normal' part that's hard for me. From the inside, I'd say that my negative emotional state is decidedly non-normal, frequently counter-productive, but mostly rational. I'm in my late 30's, in a fine long-term relationship, and unhappily running a promising but struggling small company. Most days I'm miserable but quite productive, the mental health equivalent of a functional alcoholic. I feel I'd easily convince a mental health professional that I'm clinically depressed, but I'm not sure where this will lead.
That's the goal of treatment: not to make someone ridiculously happy, but to remove the purely biological objects in the way of happiness.
My base problem might be that happiness is not a primary end goal for me. I want it in so far as it's absence makes effectiveness difficult, but I'm scared by being distracted by pleasure. What I want is a purpose I can believe in! I worry that what I really need is a complete lifestyle change, and ideally a different world in which to live. I'm torn as to whether settling for greater satisfaction with this one is a good thing.
Have you ever been on a modern anti-depressant? I was on Zoloft for about six months during a bout of really bad depression. I wasn't giddy, I wasn't exuberant, and I was still myself. It didn't make me happy. It wasn't pleasure, it's not an opiate. What it did was reduce the internal, negative dialog, and it made it much, much easier for me to focus on my work. It also made me much more willing to express myself to others, which led to better relationships.
You still have to do the work to improve things which are broken in life. If you work environment is awful, for example, it will just make it more tolerable. Your neighbor will still be an asshole, it just won't bother you quite as much.
What I want is a purpose I can believe in!
I think that's what everyone thinks they want, and what few of us achieve. Also, I think that many times, out dissatisfaction with our situation is less due to the situation, and more due to our own mental state.
I bet there's a lot in your life (e.g. long term relationship) to be fulfilled by, but you probably find yourself focusing on negative feelings around your work.
By the way, I'm very much on the same page as you regarding, "whether settling for greater satisfaction with this one is a good thing," so don't take anything I've written as condescending or negative.