website keeps disappearing and reappearing

when I google my main keyword, my website is sometimes on bottom of page1, specifically, #10
5 minutes later, I google again, and #10 is now the website that used to be #11 and my website is nowhere to be found, not on page2, not on page3, nowhere.
then 5 minutes later, I google again, and my website is #10 again and the other guy is #11 again

has this happened to anyone else? is this a bad sign or a good sign?

How long has his been happening for? It sounds like the google dance to me. This has happened with loads of my sites before. Its not necesserily a bad thing. The way I believe it,google takes your site away to recalculate it and decide where its position is going to be. When it does this to my sites,I usually end up halfway up page 1.
Are you still adding backlinks? because sometimes it also takes your site away to see if you stop linking to it.
It can also depend on how tough and competitve your niche is. Ie how strong your compotition is affects your own sites ranking
In short,I wouldnt worry just yet.

did you clear your cache? checking from browser gives me weird results sometimes that's why i use a rank checker instead.