如何重定向到上一页后点击继续作为一个客人按钮php

如果我已经登录，我在一个页面预订约会，它将预订..否则页面将重定向到登录页面，在登录页面一个选项，如继续作为客人，如果我点击继续作为一个按钮页面应该重定向相同的操作(预约与特定id-先前的搜索结果url)应该会来的。如何使用php

Following is my code:
appointment.php:
<?php session_start();
ini_set("display_errors",1);
include("config.php");
    $Doctor = $_GET['strdoc1']; 
    $my_data=mysql_real_escape_string($Doctor);
     $sql="SELECT E.EMPLOYEE_ID,E.FIRST_NAME,E.LAST_NAME,E.EMPLOYEE_EMAIL,E.PHONE_NUMBER,E.MOBILE_NUMBER, E.USER_IMAGE,
     E.EMPLOYEE_EDUCATION,E.EMPLOYEE_SPECIALIZATION,E.EMPLOYEE_EXPERIENCE,
     EA.APARTMENT,EA.DOOR_NO,EA.STREET,EA.AREA,EA.LANDMARK,
      EU.EMP_UNIT_ID,EU.EMPLOYEE_IN_TIME,EU.EMPLOYEE_OUT_TIME,
     U.UNIT_ID,U.UNIT_TITLE,U.UNIT_ADDRESS1,U.UNIT_ADDRESS2,U.UNIT_STREET,U.UNIT_AREA,CO.COUNTRY_TITLE,S.STATES_TITLE,C.CITY_TITLE,
     U.UNIT_LANDMARK,U.UNIT_POSTAL_CODE,U.UNIT_PHONE_NUMBER1,U.UNIT_PHONE_NUMBER2,U.UNIT_FAX_NUMBER,U.UNIT_CONTACT_EAMIL 
     FROM EMPLOYEE_UNIT EU 
     INNER JOIN EMPLOYEE E on E.EMPLOYEE_ID=EU.EMPLOYEE_ID
     INNER JOIN UNIT U on U.UNIT_ID=EU.UNIT_ID
     INNER JOIN EMPLOYEE_ADDRESS EA ON E.EMPLOYEE_ID = EA.EMPLOYEE_ID 

     INNER JOIN COUNTRY CO ON U.COUNTRY_ID=CO.COUNTRY_ID
     INNER JOIN STATES S ON U.STATES_ID = S.STATES_ID
     INNER JOIN CITY C ON U.CITY_ID=C.CITY_ID
     WHERE EU.EMP_UNIT_ID = '$my_data'";

    $result = mysql_query($sql) or die(mysql_error());
    $row=mysql_fetch_array($result);
    $query="SELECT DISTINCT UNIT_AREA FROM UNIT";
    $result1=mysql_query($query); 

$patient="SELECT * FROM PATIENT WHERE PATIENT_ID='".$_SESSION['PATIENT_ID']."'";
$r=mysql_query($patient);
$ps=mysql_fetch_array($r);

?>
 <?php if($_SESSION['PATIENT_ID']) { ?>
            <a href="appointment" class="appointment" title="Book Appointment">Book Appointment</a>
            <?php } else { ?>
            <a href="login" class="appointment" title="Book Appointment">Book Appointment</a>
            <?php } ?>

login .php:
 <a href="signin.php">New Patient Registration</a><a href="">Continue As a Guest</a>
        </div>