Email RECOVERY

Hello,
For some reason I have been loosing all my emails from all my folders from my gmail account. I have saving emails filed in folders since 2009. And yesterday I saw all the folders empty. I had some very important emails saved and filed in the gmail folders they are all gone. This happens to me last month too and some one helped me to recover them back. I recover all and they all came back in my inbox and it took me 1 month to put them back in all the folders and as soon as u finished doing this I lost them all again. What is going on? Is there anyway I could prevent this from happening again?