According to Stanford's sleep clinic something like 25% of people diagnosed with ADD/ADHD actually have narcolepsy. A real disease has an objective test of some kind while an ADD/ADHD diagnosis is entirely subjective.

(Initially wrote a much angrier reply cuz I was so pissed off)

Even with physical diseases there are often misdiagnoses and genera oversights.

There’s definitely a social aspect to certain kinds of misdiagnoses, but medicine is not obvious in some contexts. The human body is pretty complex!