Helen means: sun ray; shining light... and I'm gonna add "laser beam" clarity.
Kiddo, I'm going to TRY not to respond to anything specifically you've written, 'coz it's all really your "Truth" (even tho' mine is similar)... like the title of your thread. But I do want you to know that I'm in awe of your ability to reach right into topics and pull out the very nugget of golden truth in each one... even the stuck-on inadequate definitions of "depression" itself. You don't waste time... or get distracted... or hung up along the way to the "nugget". Speed of light. "Helen" is the antithesis of "depression". That's probably just a disguise - a defense mechanism - a way of keeping "Helen" safe from whatever rudeness, meanness, or abusive intentions have been lobbed at you, over the years. Put simply: depression isn't "who you are"... not necessarily part of your DNA...
I see you assembling a toolbox of truths and insights, the supplies you need to begin "creating" a way to your "Essential Self". I've read a lot of really good ideas and creative, sensitive, high-level thinking... I hear emotional energy building...I think you're probably well on your way, already... but this kind of progress usually doesn't manifest itself visibly, and doesn't "announce" itself, until awhile after it's "established".
OH... and I think there is such a thing as real happiness; joy. I think you know that too... and that's why the "fake" version is so f'ing irritating... feeling/being our real emotions makes others uncomfortable, sometimes and they want to cajole us out of it - but hey, that's THEIR problem. When we're grumpy - we're grumpy; so what? We'll get over it... in time. But there is a "phase", of getting to know those emotions all over again - and that includes the positive ones, too, at some point. That requires immersion in them. And it's IMPORTANT.
I think technically, "depression" is when you don't really feel anything or the range of feeling is restricted; shrunk down to some teeny tiny, limited, "night of the midnight sun" continuum. You're on the path of growing that continuum bigger, I think.
OK, I failed my own intention again!

I got into specifics!
10 lashes with a wet noodle for me from the smurf-brigade!! And jeez, I hope my obeservations are right... or at least close.
Sorry bout that... I'll shut up now... and await the next installment.
(((Helen)))