Would it be feasible for someone with ADHD to have no trouble concentrating?

On another thread, @ibstubro and I were talking about the characteristics of ADHS. I often tap out rhythms with my fingers, feet, or teeth. I seldom notice changes in my environment, and I’m not good at listening attentively.

OTOH, I really don’t have trouble concentrating. I study pretty efficiently, I’d say. When I need to sit still, I can, with some difficulty. Would I be able to do these things if I was suffering from ADHD?

I realize a doctor’s assesment is the only way to know for sure. However, my knowledge of psychology is minimal at best, so for now, I’d be interested to find out what you think.