From top position to page 6? That sounds like more than a couple of places. Please clarify.
Also, are you certain that this drop was due to Panda - that is, it happened on July 24? There are many posts around here about the "wrong page" ranking and it is a relatively common situation. However, the degree of drop for your home page (if I understand correctly that it really went to page 6) sounds like your home page has been hit for artificial backlinks.