As one who has had injury induced seizures since 1965 when I was 10, there are a few things to consider. His brain is still maturing until he is about 25. With proper care, he may grow out of these episodes. His concussion history is likely adding to his problems. My seizures are all related to my concussions.
His fainting problems sound like vasovagal syncope. Check out wiki at http://en.wikipedia.org/wiki/Vasovagal_response
It is easier to read that the Mayo info on vasovagal. Note the trigger of medical procedures. I was very sensitive to vasovagal during my young years.
My biggest concern is his reaction to stressors and startles. His head is put at great risk by this situation. The fall on the tile floor may not have cause serious concussion symptoms but likely did impact his brain in a bad way.
There are biofeedback and neurofeedback therapies that may be able to help him with vasovagal syncope. Teaching him to tolerate startle and stress will allow him to be much safer in his life. He needs to not be driving until this is resolved. I had to delay getting my drivers license until my condition was under control. If he volunteers to not drive until this is resolved, he may be able to avoid having his license pulled by a doctor's call to DMV. A walking EEG with attempts to startle him would be interesting.
Epilepsy meds will not likely stop vasovagal syncope. It would be quicker and less expensive to rule out vasovagal that test for seizures. The tests Sue lists can cost $10,000 to $15,000, especially if done inpatient. Even then, they can be inconclusive. I have had them all with an inconclusive result. The tests that were most valuable was a qEEG, quantitative EEG, using 18 leads and analyzed by a computer using the Lexicor database and later the Simpson-Heyrend database. There are plenty of good comparative databases used by qEEG clinicians. The challenge is finding a good qEEG clinician. My qEEG clinician could tell me how I was reacting to triggers before he knew/read my medical history. It was uncanny. qEEG uses triggers/stimuli that go beyond the classic EEG stimuli.
If you post the area you live in, I can research a good qEEG clinic for you.
btw, when I was his age, I was first put on Dilantin (phenytoin) that worked good except it messed up my gums so I was switched to phenobarbital which worked just as well. I was able to go off meds for 25 years then needed to start Neurontin (gabapentin).
Once you find the solution, whether it is meds or some other therapy for vasovagal, he should be fine.
Has your son undergone any changes in personality?
My best to you.