For my major keyword the google position of my site was 12 several days ago. Now google pulled my site down to about position 500. I don't know why. I'm really sadly.
SERPS fluctuate, there are plenty of variables that come into the equation, so without more info it's hard to tell why it happened. *Sometimes even with plenty of data is hard to determine why a specific SERP fluctuation occurred.
The only thing I changed in my site was that I replaced the Firefox referral code with a clickbank product banner.
Please don't be sad... living in google causes one important thing - don't be hasty and wait wait wait. Make all the other things to do and wait, few days for G is really a little... if you didn't nothing really wrong, it will be back.
I think you should work on your website more and fluctuation happens and for that u should not think that much...it will come up..just keep the work on... Regards Puneet M