My website was having some 2000 indexing which gradually decreased to 1500 and now it is in hundreds. Dont know what wrong i did?
Google recently released an update to it's search algorithm called Panda. It targeted websites that did not have unique content, your website may have been targeted by Panda. If you can highlight which pages may have been dropped from the index and change the content on them so it is unique or different then re-submit a sitemap to Google webmaster tools you may find your indexation numbers increasing. HTH
I did this before as well but this time i tried some thing different and it worked. The indexing is increasing now.