I have some very competitive keywords that I suddenly dropped from pages 2-3 to 35 without changing much on my site. Is it possible I could have been hacked and had bad outbound links placed on site. Is there a way to know if someone has placed invisible links on your pages?
Rankings fluctuate all the time naturally. It doesn't necessarily mean that something sinister happened. It could of course be a conspiracy by Google after they discovered what you did with those cookies.
hooperman is right so many things cause fluxuations and many times the change doesn't stick that long so you might be back where you were soon if you haven't broken tos or made major changes. I like the yellowpipe firefox addon for quick checks of various pages as I explore around. It will show visible and hidden links.
you could do a site:yourwebsite.com check to see what is showing up I have seen a lot of websites hacked, and are being used for a deceptive redirect.
maybe there's an update in google (though google regularly updates) that's why are keywords are keeping on moving. i think this is very normal. and in no time your keyword would return to it's top position.