It could be anxiety for sure. Also check out sensory integration disorder as these can be symptoms of this nervous system issue as well. Good luck. Your poor son feels terrible inside and needs some help finding out why.
I suspect your son is suffering from anxiety. I might suggest you google the phrase "children and anxiety" or "anxiety disorders in children" or similar words/phrases. If you feel that the descriptions remind you of your son, then you need to consult your family doctor. If your doctor is not able to help you, then ask for a referral to a medical specialist with experience in anxiety issues. If anxiety is the case, I assure you that your son will not outgrow it nor will it go away. I wish you the best ....