Robert_Charlton - 11:37 pm on Sep 18, 2013 (gmt 0)
Any change in the layout of the serps page occurring around then that might have affected you? That has been known to have caused traffic drops in the past. Have the image carousel results come to your niche? That's a possibility.
It sounds like you might be looking at only very obvious keywords, though. Have you been tracking long tail queries? Any drop-off in traffic from those?