My Son Has Fainted About Once Every 4 Years- He

My son has fainted about once every 4 years- he sees bright lights and everything goes blank before he faints-- he is 6'3" and is thin and is on ADD medicine and have felt that this sometimes happens when he hasn't eaten -- yesterday it happened after he ate and was just wondering if he should have a work up of some sort? He had an MRI after he had this when he was 5 and it was normal.