I think it's actually unnatural for us to sit so long, especially males (as evidenced by females' larger buttocks adapted for sitting more than small male buttocks).
Rigid classroom seating arrangements (and office setups) are themselves stifling to a great number of people no matter what their brain chemistry is. I think it's just a natural reaction to an unnatural environment that inherently exacerbates feelings of discomfort, especially for certain individuals.
I bet it wouldn't seem that odd at all for you if you were a hunter-gatherer. The tribe would probably encourage it because of the innovations you would be responsible for due to your curious wandering.