Have you heard the phrase "absent seizure"? It's not a gran mal seizure that you see on TV. It's like they are doing something, blank out for a few seconds, then return back to what they are doing like nothing had happened. My son has them and it's very hard to distinguish that from inatatention. But if you look on you tube you can see some examples that have been posted. Of course an EEG didn't show anything. The other thing I notice is that my son gets very bad behaviours right before and it's like the absent seizure resets him. This may not be what your son has, but it might be worth looking at.