Over the last week, Google has been testing what appear to be some significant algorithm changes, which have cause significant changes in ranking for a variety of sites.
There are some facts and opinion below, but first I want to make sure you have some tangible actions.
Check to see if you’re affected, and by how much. Do a quick search on Google for your brand name, domain name and for any high-volume head terms. If you find that you are not ranking on the first page for your brand name, or if other terms have significantly slipped in rankings, then it’s a likely sign that you’re suffering. Looking at your analytics will give you more insight into how your total organic traffic is looking. This will also help you find out when your site first suffered. Don’t panic, and don’t make any sudden movements. It might feel like the sky is falling around you right now - particularly if your traffic for a particularly valuable term has just slumped to zero - but an immediate response isn’t likely to be helpful.