Hi, I found recently the google index position change violently, one of my site's keyword position changing status is page13(the day before yesterday)-page 24(yesterday)-page 14 today(today). Have you encounter the same question?
Sites with less quality content are being affected(in terms of rankings) these days. So, it is in your best interest to add fresh and quality content on your website.
Google has recently updated their algorithms,due to this your index position is changing and also you should check your site's content ,if it is duplicate or copied,then change the content and post original content on your site and also,check the quality of your backlinks. Try to get backlinks from quality and high PR sites,then only you will get good rankings on SERPs.
You don't have to worry about it if you think your keywords have been ranking consistent at the top before. You just have to wait especially now that Google is performing betas for their new algorithms and which mean they are not permanent and subject for further improvements.