my site's ranking has gone down - as has many others' due to the current google update going on. but i wonder if in my case it is because my site was hacked by spammers recently. somebody inserted many files in some folders inside my site. these html files inserted by them had refresh redirects and pointed to some gambling, poker and other such sites. and many spam sites have put these links. a google search for 'niponwave' (my site name) will show them as results. i was late to discover this and it has been like this for 15-30 days until i removed the files few days back.
There is always updates going on at Google. Don't worry about it, and focus on getting your site back up again! And make it a little more secure this time..
Google updates are performed every 3 months. So, if you continue with good work, you'll get your ranking back for sure!
Use security tools on your site To prevent spammers from unauthorized entering.... and update it again... .