There are several things that can cause the symptoms you describe, Anexiety, Costeochondritis, Pleuresy. low grade respiratory infection.
If the symptoms are concerning you please take your son to a doctor
First I would try going for gas build up in his chest.this often effects the heart a
nd lungs,causeing sinus tacheycardia and anxiety,causeing lack of oxygen to the body.sometimes it just happens,and sometimes theres somethong bigger causeing it.See how he feels after that,then prceed from there.Good luck