I really was not functioning very well, for large periods of time. I scaled back my original post because it felt self-indulgently long, but I'll try to explain a little more.
Initially, as a teenager, it was mild stuff like losing things with an unusual degree of frequency, to the point where it was a bit of a running joke as between friends. Of course, losing your bank card, drivers license or whatever else, even if it is 10+ times per year, is a pain but probably doesn't render you "non functioning".
By my later teens though to my 20s, though, the most challenging standalone symptom was the insomnia. It would not be unusual for me to go 2 or 3 consecutive nights without sleep. I would be exhausted, I would want to sleep, I would adopt good sleep hygiene practices, I sought conventional and not conventional treatments but my brain would just race and race, even if I didn't feel particularly stressed about anything.
It was one of the primary drivers of my extremely low attendance, caused me to become socially withdrawn and made me decide to prolong my time in higher education (because I didnt see how I would be able to hold down a 9-5 job). I can say with comfort that I had the lowest attendance on every course I undertook. It wasnt just insomnia, it was also an inability to stick to a timetable (forgetting classes, or going to the wrong place at the wrong time). I can promise you that I wanted to be present, to apply myself, to attend social events, but one way or another, I would fail to.
Housemates and the friends I did maintain would find me frustrating to live with, as my disorganization was extreme. I found it embarrassing, but would make the same mistakes again and again.
When I started living indecently, the personal safety aspect of it became a concern. Things like leaving the stove turned or iron turned on (starting multiple fires - to the point I stopped using those appliances), failing to lock the door (or locking myself out, needing to make out of hours calls to my landlord or call a locksmith. Frequently arriving late at work (a constant source of negative feedback and once, job loss).
One of the reasons for my excessive and repeated lateness was that, so frequent were my instances of forgetting to turn something off, or lock something, that I started to find obsessive compulsive thoughts a huge challenge. Leaving the house often became a 30-60 minute ordeal, in that I would check everything, leave, but then wouldn't be able to remember with confidence that I had turned things off or locked things, so would turn around and go back home, and check everything again. I was, though, so doubtful of my memory that I would often find myself going back multiple times in a morning.
I tried various coping strategies but did actually find one that worked for me, with the advent of camera phones (basically, being able to video myself going through the "leaving the house" checks, which i did for about a decade).
I stopped driving because my inattentiveness also made me unsafe. I didnt race around or anything, it would be stuff like stopping at a red light then, for whatever reason, absent mindedly starting off again, with the lights still on red.
I mentioned it a few pages back but (to me) an illustrative example relates to a much loved pet. I'm hyper focused on my pets (don't shut up about them, despite how much I can tell nobody cares). To the extent I am focused on anything, it ks their well-being. When one was sick, and needed medication (which needed to be kept in the fridge), I ruined 4 bottles (by leaving them out) in 5 days - despite straining to remember (even repeating, aloud "meds go back in the fridge" on loop, only for the thought to drop out of my head). Each time, I had to take time out of work to buy a replacement bottle. It was actually this - and the fact that it is representative of many other day to day tasks- that prompted a colleague to "diagnose" me.
I do wish I could have my colleagues post on here because, even with medication, the frequency with which I lose my key or my pass is a constant source of frustration and inconvenience to others. I likely account for 95%+ of instances accross the team. A lanyard has recently been imposed, to cut down on how frequently i have to disturb others outside of office hours. Colleagues have also made reminder posters for my door and, the last person to leave before me each day (I'm usually last out) will always come to check if I have my keys.
And yet, my persistent lateness, disorganization, constant admin backlog and alike is (sometimes, through gritted teeth) tolerated, because I'm very strong at my strengths.
What scale would I propose? I don't know, but I can tell you that my inability to reliably complete simple actions, and keep track of belongings, has been a constant source of criticism and frustration from friends, family members and coworkers. If 100s of people all tell you that you are extremely deficient in an area, and that they've never met anyone worse, then (1) they are clearly judging me by some set of criteria, and (2) it'd be strange for me to to take heed.
As mentioned, the diagnosis has mattered in that its encouraged my employer and I to find accommodations. It also helps my self esteem (as, to, does my improvement on medication). It has also improved my self esteem because I can better understand my persistent and embarrassing failures at the basic aspects of day to day living, despite being able to easily perform very complex tasks.