Thank you, all your comments are helpful. He has not had any further fainting spells since the last one and has been well with no colds etc. Hopefully it is none of the above!
There are epileptiform seizures (i.e.: epilepsy) and seizures from other causes, as well as "seizure-like events" that occur for various reasons. An EEG is useful for evaluation but unfortunately not all that reliable. A 24-hour video EEG or even a 72-hour ambulatory EEG may be necessary in the case of your son. A brain MRI, ideally 10T with contrast, is something many neurologists would also likely consider.
Your son's "attacks" seem to resemble nacrolepsy or similar sudden losses of muscle tone with alterations in or loss of consciousness. Some seizure disorders, e.g.: complex partial seizure disorders, present this way.
Make certain to find a neurologist who specializes in the brain and central nervous system as opposed to one that works on neuromotor issues. The Epilepsy Foundation (epilepsyfoundation.org) should be able to help you find one locally.
Hope you can get through the evaluation quickly and find a resolution.
The way you describe his symptoms isn't classis Epilectic Seizire activity, but it very well could be. Get a CT/MRI of his brain to rule out anything Neurological,and if you can, make it sooner rather than later. Best Regards.
My son has seizures. They are really tricky sometimes to diagnose. We never knew our son was having mild seizures until he had one when he was 12. We took him to a Neurologist and they couldn't find what was causing them. 3 years later he had another. The same story, nothing. He told the doctor about twitching whenever he was concentrating hard on things. He would read and start twitching or jerking a little then it would stop. We finally have him on medication and he is doing well. I hope you can find out for sure if it is epilepsy or not. It is so hard sometimes to know for sure.