How can add and adhd be the same disease, if one is so hyper?

Not a disease: Add & adhd are psychiatric labels, they are not diseases. There is no blood test or x-ray to prove someone has it. The diagnoses is made from a checklist which is subjective. One person can look at the child and think he has adhd and another can say "no", he doesn't. It is better to find the real cause such as learning problems, allergies, diet or nutritional deficiencies.

Same brain area: The main difference between add and adhd is the h - hyperactivity. Hyperactivity is a feature that can occur with attention deficit disorder. Some people have it, others don't. We see hyperactivity more in boys, whereas inattention occurs more in girls. The core of adhd is the inattention and impulsivity.

Same thing: Adhd is a condition of inefficient brain management. This means that brain activity is mismanaged. Too much or too little activity is the the same neurologic thing. Too much focus or too little focus is the same thing. These are just names that have been used in the dsm-iv-tr manual. Previously there was a distinction made between hypertactivity present or not. Now we no longer make it.