Is Sudden Vision Loss Along With Unresponsiveness Signs Of Blood Sugar Fluctuation?

My son was drinking at a bar with friends and all the sudden laid his head on the bar. A few of the girls were nurses and became worried and called us. He was pale, had lost his vision, said everything was white, couldn t move and two of the guys carried him outside. He was bad for about a half hour and when he came to, he said he could hear the nurses talking, but couldn t really respond. How do we know if he was drugged, or if this was some kind of blood sugar thing?