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ADD or in simple Hyperkinetic disorder
is a constellation of symptoms of Inattention, hyperactivity and impulsivity. ADD is a childhood psychiatric disorder.
Usually in simple terms it is said that child with ADD is said to be on foot only, he can't sit still and usually can't wait for turn. But as you have mentioned that you were able to study even continuously for 5 hrs, and you are complaining of inattention so as per my opinion we can think of other possibility as-
- as inattention may be a manifestation of depression
, in depression individual fails to focus on one thing and usually have other features like decreased interest, energy and low mood.
- as a part of anxiety
disorder, in severe anxiety states there may be inattention.
so try to consult with doctor about these possibility also.
Hope I cleared your doubt.