Euphoria is low unhappiness and high happiness.
Depression is high unhappiness and low happiness
I can't really come up with what it would mean to be high unhappiness and high happiness. Manic, maybe? It sounds like a very confused situation.
Having both created a startup and worked a cushy job, I can relate
I rarely (if ever) comment on my mental health online, but I can totally relate to a X-Y quadrant as you describe. Many mental health professional debut their appointment with a dreaded question "how are you feeling today?".
If I had this diagram with me, it would save time and be way more descriptive of my state of mind.
As for the high unhappiness/high unhappiness quadrant: I'm not manic myself but know close ones who are. I think it fits.
Thanks for opening my mind about this.
I am happiest when I stretch past my limits, which not un-coincidentally means I am also always hitting my limits.
Would not change anything. Might change my mind at any time though.
(I am not manic, maybe an incurable optimist.)
Manic is kinda weird. The above makes it sound almost good, or kind of good. It is not. It is very dangerous. You do not want to be manic. (But you might, maybe, some of the time, want to be hypomanic.)
(Disclaimer: I have had contact with mania in my life but have never personally experienced a Bipolar I manic episode and I aim to keep it that way.)
It's like that.