If your website traffic suddenly drops and you see a corresponding decline in rankings, there is a good possibility that you are on the receiving end of a Google penalty. Google reported in 2014 that over 400,000 manual actions are taken against websites every month by their web spam team (1), and that's really only a fraction of the total number. Many other websites are penalized when Google rolls out new algorithmic updates to Penguin or Panda.
A sudden, unexplained drop in rankings can be disastrous for retailers, as it can prevent visitors from finding and purchasing your products, but you can recover from a Google penalty. The first thing you need to do is find out what the cause is.