Puedes hacer esto:
Código PHP:
if ($row= mysql_fetch_array($Query)) {
$from = $_SERVER['HTTP_REFERRER'];
if( empty( $from ) ) {
$from = "index.php";
}
session_start();
$_SESSION[auth] = true;
$_SESSION['userid'] = $convertido; //stripslashes($row["userid"]);
$_SESSION['nombre'] = $row["nombrecompleto"];
$_SESSION['email '] = $convertidomin; //$row["email"];
$_SESSION['nombrec'] = $row["nombre"];
header("Location: $from");
}