novemh - 4:17 am on Oct 18, 2012 (gmt 0)
actually there was an update on Google's algorithm last May 16, 2012. They rolled- out the "Knowledge Graph", however I can't see any relation to it with the sudden change in your traffic. But there are other factors you need to consider why your traffic decreased. Try checking out the quality of your inbound links. Are they of quality and relevant to your website? Do you have duplicate content pages?