tedster - 6:36 pm on May 6, 2013 (gmt 0)
Something is inexplicable like a mass behavior. When search results haven't really changed, then what would cause traffic drops and lower sales?
One possibility is a change in Google Search's auto-suggest. Results for YOUR TARGET SEARCH may be the same, but because a drop-down list change, fewer Google users are choosing that option.
If you don't track this kind of thing regularly, you may never notice it until the External Adwords tool changes a few months down the line. It can change with a new demand of any kind, based on current interests, broadcast and print interests, etc.