netmeg - 8:04 pm on Aug 16, 2013 (gmt 0)
There are various reports of this - if you page through this forum, you'll see several posts.
Google has stepped up their "invalid clicks" reporting, so that it happens almost instantly as opposed to at the end of the month. It sounds like you might have a lot of clicks being reported as invalid. While your traffic might come from Google referrals, you might want to look to see what parts of the world it's coming from (is the geo mix the same?) and also at your mobile traffic (is the mix there the same? Does your site render ads well on phones?) to see if any of that has changed.