Before you sound the alarm and get lost down a rabbit hole, you should make sure that the drop you’re seeing is actually real. This involves answering two questions: A.) Do you trust the data? This might seem trivial, but at least a quarter of the traffic drops I’ve seen were simply due to data problems. B.) Is this just normal variance? Metrics go up and down all the time for no discernible reason. One way to quantify this is to use your historical standard deviation for SEO traffic. Get the full story at MOZ