My boyfriend is a 21 year old male, and experienced sudden dizziness, blurred vision, and a feeling like he was going to faint while he was driving. He had eaten a typical amount of food beforehand and was hydrated. He does not have a history of any medical conditions or allergies, and is not otherwise sick. He exhibited no other symptoms. He is about 5'5" and 135 pounds. The symptoms were severe enough that he had to pull over, and he then called an ambulance to check his vitals, which were all normal. What could have caused this?