Get Next or Previous Post (Looped). Will continue working once end of posts reached.

previous-next-post-looped.php

<?php
/**
* Gets the next post in the current post type, even if is last post
* Inspired from https://gist.github.com/banago/5603826
* 
* @method get_next_post_looped
* @return WordPress Post Object
*/
function get_next_post_looped() {
    $post_type = get_post_type();
    if ( get_adjacent_post( false, '', false) ) {
        return get_next_post();
    } else {
        $loop = new WP_Query( 'posts_per_page=1&order=ASC&post_type=' . $post_type ); 
        $loop->the_post();
        $postToReturn = get_post();
        wp_reset_query();
        return $postToReturn;
    }
}

/**
* Gets the previous post in the current post type, even if is last post
* Inspired from https://gist.github.com/banago/5603826
* 
* @method get_previous_post_looped 
* @return WordPress Post Object
*/
function get_previous_post_looped() {
    $post_type = get_post_type();
    if ( get_adjacent_post( false, '', true) ) {
        return get_previous_post();
    } else {
        $loop = new WP_Query( 'posts_per_page=1&order=DESC&post_type=' . $post_type ); 
        $loop->the_post();
        $postToReturn = get_post();
        wp_reset_query();
        return $postToReturn;
    }
}