It's tough to say what the cause may be.

It could be biological, psychological, or a combination of the two. Do you take meds for the ADD? If so, med side effects are a possibility as well. I know that I didn't really answer your Q, but I think that there are a lot of possible causes and wouldn't recommend leaning towards any one particular cause just yet.

Rule out the dangerous possible causes first, and go down the list from that point. That's the way that I'd go about it anyway.

Best wishes to you....take care!