Hmm, this is a pretty good chart and is meaningful to me. Earlier this year I think I got somewhere between "exhaustion" and "burnout" which was not pleasant, but seeming better now. I think I'm still somewhere in the "difficulty concentrating" to "confused" region.
I am however concerned about the placement of "irritable." As I get more anxious and confused, I generally get less irritable, because who am I to complain about you being stupid when I'm busy being stupid? I find my irritability is somewhere near the "optimum" level. Too bad for y'all when that happens. :)
I think the question that's generally not adequately addressed is whether it's good to be optimum at delivering on moderate demands, or sub-optimal at delivering on much more difficult demands.