What is this kind of “Google Dance” ?

Do you experience this kind of weird Google Dance as well?

Look at this:


I was in the #10 for a few months and in the last few weeks on #1, but then some keywords jump to #90+. Just saying I didn't build any backlink since around two weeks and when I built backlinks it were in a very small amount.

Anyone of you…

What is this kind of "Google Dance" ?