Get Value of Post before

<?php 
$previous_post=null;
    if ( have_posts() ) {
        while ( have_posts() ) {
            the_post();
             global $post;
            if($previous_post!=null)
            {
              /// Do what ever you want to do with previous post $previous_post.
            }


                  $description = get_post_meta( get_the_ID( ), 'metabox_description', true );       
                  echo $description;

                  // Add: echo $description_from_post_before;
            $previous_post = $post;
        } // end while
    } // end if
?>