I have a feeling it's the same thing that happened a month ago, my site dropped to the same positions back them too and then recovered after a couple of weeks. Fingures crossed this is the same as my site spends a lot on ppc so it's not a adwords factor. Google are targeting more sites to take up ppc but thats normal. But it survives because of natural search so doing this does not make sense especially when I am seeing different rankings every 5 mins.
Facts are that even mjor branded websites who do pay millions on ppc have been knocked down. The ones that have stayed are sites with strong deep links. This may be a big factor in the latest update.