What Causes Blackouts And Memory Problems?

Over the last two months my friend has started to experience blackouts / periods where he cannot remember doing things. Yesterday he felt sick in a car but thought all was well when he arrived home to be told that he had been sick all over the car and that the driver had to stop for a period of time by the roadside. He does not remember any of this. He is now scared. My friend is 48 with no medical problems or history.