You are right in that discontinuing ADHD medication can lead to withdrawal symptoms.
But you are dead wrong in that ADHD does not disappear after withdrawal. As it would if it were a drug addiction.
ADHD was there before taking medication, and it will persist long after stopping medication. (If we assume the diagnosis was correct.)
Other psychiatric medications are often withdrawn slowly. For example, a patient on weekend leave in hospital would be called straight back to the ward if they lose their prescribed benzodiazepines e.g smashing a bottle of solution, due to withdrawal. Especially the case if used during alcoholism detox, where the seizures could kill otherwise.
Many of the symptoms also do not go away with medication. It's not a magic bullet. It just raises the floor a little bit so things are easier to manage. Some days the medication doesn't help all that much if other things off set it.
No?
Because you ran out of heroin.
That is what my life was like. If that doesn't sound like a medical condition to you, then I don't know what you're thinking.