Domain going strong since 2009. Wordpress site since this March. Traffic (impressions and clicks), CTR, SERPs, pagerank, mozrank, domain authority, page authority, no. of pages (100% in google index) all up and up every month. All white hat SEO.
I predict it will go back to normal in a week or so, so not overly concerned. Just strange as have not seen such a drop in a very long time on our site.