An American woman born in Indiana suffered a stroke and woke up with a British accent. According to the doctors in the article, Foreign Accent Syndrome is a rare condition caused by brain damage. According to me, this story sounds like it should be in The Onion.
I used to work with a girl who would fall into a British accent when talking about movies and books. I think she thought it made her sound sophisticated, like wearing glasses with plain lenses in them.