I failed freshman composition 3 times in a row since it was the only class where tests were not part of the grade.
As an adult, I find that laziness had become a learned behavior. I was smart and generally easy-going meant that none of my K-12 teachers were willing to flunk me, but getting an A seemed out-of-reach. This meant that I could "get by" with minimal effort, while intense efforts didn't result in obviously visibly better outcomes.
I eventually found a good therapist (though Sturgeons law definitely holds for therapists) and have been sorting things out since.
As far as "getting by" and laziness as a learned behavior, I always worked hardest on my hobbies throughout K-12, so as an adult I've gotten to the point where my hobbies have become my careers. I started building PCs and running Linux on my own in High School, along with playing music, so now I'm a software engineer/musician. Software is one of the few careers where you can go on an insane research binge on a whim and actually be praised for it, and performing music is one of the only things that I've ever done that fully quiets my mind. Something about the adrenaline of being on a stage really helps with my ADHD-Inattentive type; guess it's just like a stimulant.
"Do what you love and you'll never work a day in your life", etc
Having the correct label helps some people get their uncooperative body to be productive enough to make life suck less. Just calling it "laziness" generally suggests zero real remedies and often leads to the beatings shall continue until morale improves.
The fact I may have an incurable mental illness (and that I could be branded as such) terrifies me.
Plenty of people with ADHD choose not to take medication though, and I'm having trouble coming up with a situation in which a judge would order you to take it. As long as you're not blaming your ADHD as a reason you broke the law (which you shouldn't, ADHDers may have poor impulse control and bad executive function, but we still need to hold ourselves accountable for our actions), I don't see where it's the law's business if you have it or don't, or medicate it or don't. There are plenty of non-medication coping strategies, including therapy and coaching.
Underachieving is just inability to deploy your efforts effectively, or even inability to muster an effort in the worst cases. That translates to every domain and aspect of human life from scholastic to social to friendships etc etc etc.
Value is not entirely subjective.
Welcome. We call it, life.