If you have a website, you will notice sometimes the ranking position suddenly jumps like from page 1 to 5 then go to page 2 and then return back to the same position. It is often referred to as fluctuation often blamed when they updated their index.
Same scenario seen when they work on their data centers during PR updating. It can show the actual one and fluctuates between the previous.
It's not related to google dance but merely stressing a point saying that it is just a common thing which is nothing to worry about.