PHP obtiene URL anterior
$_SERVER['HTTP_REFERER']
Average Angelfish
$_SERVER['HTTP_REFERER']basename($_SERVER['HTTP_REFERER']);//This should be on the previous page
session_start();
$_SESSION["url"] = "the_url_of_page_we_want_to_get_back.php";
//This should be on the current executing page
session_start();
$previous_page_url = $_SESSION["url"];