A 43-year-old man fainted suddenly, while walking home from work. There were no prodromal symptoms. The episode lasted for only a few minutes. He was not confused or drowsy afterwards. He had no other symptoms. His medical history and family histories are unremarkable. He is not on any medications. He does not smoke and only drinks socially. There is no history of substance abuse. His full blood count, random capillary glucose, serum electrolytes, and chest x-ray are normal. Serial ECGs are also normal.