FazK - here is a link to one of 1000s of articles in reputable publications which explain that brain scans and neurological breakthroughs offer definitive evidence of ADHD and the positive effects of stimulant medication.
Brain Imaging Data of ADHD - Psychiatric Times
It is naive at best to suggest that you know better than mental health professionals about the existance of neurological disorders. Furthermore would you simply suggest that a diabetic merely change their diet and concentration and levels of discipline? The pancreatice, adrenal, thyroidic hormones all effect neurological responses. That you have not experienced ADHD does not make it a non-entity nor an illusion any more than your not experiencing any other disease makes them fictitious.