I'm sorry your son isn't feeling himself at the moment, but i just wanted to throw another possibility into the mix, if you don't mind.
For many years as a child i used to have moments where i was very vague, i could hold a basic conversation, but would feel a little sick, slight headache afterwards & not really remember what the conversation was about.
These would usually last 30 seconds or so, but afterwards all i'd want to do is sleep & be on my own.
After going to the Dr's, sent to see specialists, being tested, being told it was growing pains & i'll grow out of them, 7 years later when i finally shouted loud enough at all the specialists, they told me i was Epileptic & was i was experiencing was a form of Petit Mal Seizures.
If you look up these forms of seizures, they come in MANY different forms. Most people think Epilepsy is fall to the floor & start shaking your limbs, it's not. Those are Grand Mals & are very easy to diagnose because you can actually see something happening rather than just weird feelings that you cant explain.
There are so many different seizures that Dr's sometimes misdiagnose or not even diagnose in the first place.
I used to get a feeling of de-ja-vu just before one of my absence seizures/Petit mals but when i was on medication i still got the de-ja-vu but not the absence .... i told the specialists & they informed me that this was still part of a seizure just the feeling that your going to get 1.
The mind is such an unknown thing, it's always best to get it checked out.
All i can say, is to keep on at your GP's, if you don't get the answer which explains everything, go elsewhere.