Oh dear. I'm so sorry to hear that! Do you have access to your database through PHPMyAdmin or some other tool? If so, check your
wp_posts table to see if the posts are still there, perhaps with something other than 'post' in the
post_type field. If you've just accidentally changed the post type to one that isn't registered anymore or something, they would no longer show up in your admin screens, but they'd still be in the database.
If they are, then it would be fairly easy to fix with a query. For example, here's how you would look for all posts and change them into pages:
UPDATE wp_posts SET post_type = 'page' WHERE post_type = 'post'
Just replace 'post' and 'page' in that snippet with the post types in your site, then paste that into the SQL tab in PHPMyAdmin (or whatever).