Good, it's not a sudden change.
If something like it starts suddenly it's worth getting it checked out to make sure it's not something serious. Chances are that it's just an individual thing.
I've read a load of Sack's stuff, I think you'll like him. He did steal one of the stories, about a taxi driver, who lost his memory for what was on one side of him, but tell him to imagine facing the other way down a road, and he would forget what he'd just said, and tell the names of the buildings on the side he couldn't remember when he was imagining looking the first direction.
He was an Italian prof's patient. The Italian prof was really gracious, saying that the knowledge had got further with Sacks than it would have without him.