Do you believe ADHD is real? Why or why not?

Question on Quora Answered by Schulamit Widawsky, I am a mental health professional, in private practice for decades. Here are parts of her answer. "People who are concrete thinkers, and cannot understand things they cannot hold in their hand or see, touch, hear, or smell, have difficulties understanding things that are not so easily recognized by our main senses. If someone is bleeding no one questions whether or not they are bleeding, because the blood is right there." "ADHD is over diagnosed, also under diagnosed. That is, doctors who do not study it will look at any kid who is very active and annoying, and label them ADHD, while entirely missing the ADHD kid who is quiet. All this proves is that ADHD is much more difficult to diagnose than most people realize, even doctors." "Scientists have not been able to isolate exactly what causes ADHD, but they do know it runs in families, it shows up more often in families that have a variety of mental health issues, and very often when a child is diagnosed in a family where ADHD was not previously diagnosed, a full investigation of the family will reveal a parent, aunt, uncle or grandparent who also has ADHD. As someone in my fifties, in the last twenty years, I've see most people my age and older who have ADHD diagnoses, got them because their children were diagnosed, they began learning about it, and realized it might be their issue as well. It is very common that a child gets on medication for ADHD and only then does the parent(or grandparent) finally get medicated for their ADHD."