Lost Email Content?

I have a Yahoo email account and have never had problems until today. Although ALL of my saved email is still "there", about 25% of it is now blank. If I do an email search, the preview pane shows some of the content, but when I open an email, the body is blank. Or, I can simply look through a folder, and about 1/4 of the emails have no content. I've lost some very important stuff!