ADHD is terribly misnamed, and doesn't usually manifest as physical hyperactivity in adults. It's an executive function disorder. This means things like time blindness – difficulty conceptualizing and persisting tasks into the future, and difficulty keeping short term goals in mind.

I think about it like packet loss, but for intent. With healthy executive function, one's goals and intents are persistent streams that can be held on to like a train track. (This is based on other people's description of how their mind works – I would consider that ability a superpower). With ADHD, the tracks will just fall out like a trapdoor every so often – sometimes every few seconds. You have to reinitiate the connection, but because the thing that failed is the same thing that remembers what to connect to, I have to reestablish what I want to do in the first place, and it's usually not the thing I was doing before. So I end up shooting around in semi-productive bursts, unable to see things to completion.

The other counterintuitive thing is hyperfocus – people with ADHD periodically experience the inverse. I spent nearly every waking moment in the last 3 days working intently on a software project I'm interested in. Short bouts of intense concentration (especially if you don't feel in control of their application) do not mean you don't have ADHD. They could mean the opposite.

Here's the best explanation I've ever seen of the subject: https://www.youtube.com/watch?v=SCAGc-rkIfo

My personal theory is that those with ADHD have compressed dynamic range of the dopamine behavior/planning feedback loop. Neurotypicals have a smoother control loop with more resolution. ADHD brains have less DA throughput, but the brain still tries to "crank up the gain" to compensate. The result is a response curve that's closer to a step function. Every molehill of a task feels like a mountain because the activation energy is high. Conversely, once you get in the groove, doing anything else feels like trash because the current hyperfocus is so rewarding.

Haven't found a ton of research to back this headcannon yet but there's evidence that the D1/D2 ratio is extremely important.

Thank you for that link, and that analogy. Definitely going to see about getting myself in to get tested and see if I can't get some medicine.