Hi,
My 8 years old son has ADHD, the past 4 months he has been talking to himself, shaking his head, putting in front of eyes tracking the movement and having violent outburst. I am afraid that these are not symptoms of ADHD.
I agree with the above. If he is on medication - that could be causing the problem. Particularly if he has not been on meds for much more then say 5 or so months. This is something that you definitely want to let his doctor know about - if he is on meds. They are always being adjusted as all kids are different..
If he is not on meds, then you also want to let your doctor know what is going on because this is not typical ADHD behavior.