turbocharged - 4:25 am on Oct 15, 2011 (gmt 0)
Sounds like your site has Panda Fever. Unpredictable and wild swings are common with Panda, even with well established but poorly branded sites. If you follow what Google has stated in regards to this, you might be wise to assess your site's quality. Identify and remove/strengthen weak pages, remove duplicated content/pages, etc. Also, the wild swings could be related to which datacenter is actually serving you.