Thanks for your reply.
After the first Panda update in February 2011, my site was affected but after that no major decline was seen for many months. However in the last few days I noticed a worst decline in the history of my site.
I use the domain name of my site (domain name) and its on the fourth position in Google. It was used to be on the first position since the site is launched. Also many other keywords lost their position. It seems like the end of something but I don't know the reason behind it.
I don't know its the continuation of panda or what. But again after the first major panda there was no major decline for many months and the current situation happened few days ago.
Can anyone experienced with this issue help?