My friend's elderly husband will occasionally sleep all day and not understand what people are saying to him. What's happening?

My friend gets really scared when her husband is like this. It started last January, and stopped over the summer. Now he's doing it again. The spell lasts a day or two and then he's perfectly fine again. His doctor told him to go to the ER to get a brain scan when this happens, but he refuses. What are some resources that my friend can use to help her to help her husband? What could this condition be?