I work mostly with kids with developmental disabilities (autism and mental retardation), but I have also worked with some kids who have ADHD. In the more severe cases, the disorder can be pretty obvious and medications like Ritalin can be very helpful. If you think kids like this can be cured by a good swift kick in the pants, you probably haven't met one of them.

I do agree, though, that ADHD is probably overdiagnosed and overmedicated. My perspective is maybe kind of skewed because I only work with kids who have fairly severe problems. For every one of those, there are several who are in more of a gray area. Medication should be a last resort. A lot of times, it can be very helpful for these kids to have more structure in their lives.

Adult ADHD is less common, because a lot of people grow out of it, but it is real. I always look at things in terms of basic functioning. Are you able to do the things you need to do to live a more-or-less normal life? If so, then you probably don't need to worry about this. Needing to get out of the house once in awhile is probably okay, whether because of attention problems or anxiety. But if you have such a hard time focusing that your life is in a constant state of disarray, then you might want to consider looking into this a little more. I would start with a therapist or psychologist rather than a medical doctor, and go from there.

Reading up on the subject also helps. The chart you copied is way too simplistic, but you should have no problem finding much better information.