How is it possible that one of my PR 5 sites had on google around 9000 pages crawled and all over sudden it has around 500? and it's not a new site! I didn't make any changes to the site.. what happened?
Google is just completely f'ed these days. Tomorrow you'll probably have 7000 pages indexed, the day after that 3 pages. My best advice is just to sit tight, not make any drastic changes and wait out the storm.