I Have A 27 Year Old Son. Two Years Ago

I have a 27 year old son. Two years ago be was riding a city bus and passed out. Since that time he has had random re occurrences of passing out/fainting while behind the wheel of a car, at work, just walking around. He has had blood work done and ekg's. Everything comes back normal. The doctors tell him not to drive and say he has vasovagal syncope. What would you recommend?