PHP created Main page with selection of Download two options related to Mysql Table fail to properly export file

Question

The below code is in the main page with two types selection. It has a user session login check with an else clause:

<FORM METHOD="POST" ACTION="<?php echo $_SERVER['PHP_SELF'];?>">
   <select name="type">
      <option value="Technical">Technical Records</option>
      <option value="Spares">Spares Records</option>
    </select>
    <input type="submit" value="Download Record"></input>
</FORM>

<?php
include(ABS_PATH . "/hidden/access.inc");
   if (isset($_SESSION["user_id"])) {
      if (isset($_POST["type"])) {
        switch ($_POST['type']) {
            case "Technical":
                 include(ABS_PATH . "/hidden/export.php");    
                 break;
            case "Spares":
                 include(ABS_PATH . "/hidden/export.php");
                 break;
        }         
    } else {
        echo "please select download option";        
    }
} else {
    echo "Please Login First"; 
    function redirect($url) 
    {
        ob_clean();
        header('Location: '.$url);
        ob_end_flush();
        die();
   }
   redirect('login.php');
}        
?>

The sub download page has PHP code to download from a specific table, where its name is included in with the Database connection username, db name, pass Table name etc.

One of the two sub-pages for download are as below code:

<?php
//session_start();
//define("ABS_PATH", $_SERVER['DOCUMENT_ROOT']);

if (isset($_SESSION["user_id"])) {
/*******EDIT LINES 3-8*******/
//include '/hidden/access.inc';
include(ABS_PATH . "/hidden/access.inc");

//create MySQL connection   
$sql = "Select * from $DB_TBLName";
$Connect = @mysql_connect($DB_Server, $DB_Username, $DB_Password) or die("Couldn't connect to MySQL:<br>" . mysql_error() . "<br>" . mysql_errno());
//select database   
$Db = @mysql_select_db($DB_DBName, $Connect) or die("Couldn't select database:<br>" . mysql_error(). "<br>" . mysql_errno());   
//execute query 
$result = @mysql_query($sql,$Connect) or die("Couldn't execute query:<br>" . mysql_error(). "<br>" . mysql_errno());    
$file_ending = "xls";
//header info for browser
header("Content-Type: application/xls");    
header('Content-Disposition: attachment; filename='.basename($file));  
header("Pragma: no-cache"); 
header("Expires: 0");
/*******Start of Formatting for Excel*******/   
//define separator (defines columns in excel & tabs in word)
$sep = "\t"; //tabbed character
//start of printing column names as names of MySQL fields
for ($i = 0; $i < mysql_num_fields($result); $i++) {
echo mysql_field_name($result,$i) . "\t";
}
print("\n");    
//end of printing column names  
//start while loop to get data
    while($row = mysql_fetch_row($result))
    {
        $schema_insert = "";
        for($j=0; $j<mysql_num_fields($result);$j++)
        {
            if(!isset($row[$j]))
                $schema_insert .= "NULL".$sep;
            elseif ($row[$j] != "")
                $schema_insert .= "$row[$j]".$sep;
            else
                $schema_insert .= "".$sep;
        }
        $schema_insert = str_replace($sep."$", "", $schema_insert);
        $schema_insert = preg_replace("/\r\n|\n\r|\n|\r/", " ", $schema_insert);
        $schema_insert .= "\t";
        print(trim($schema_insert));
        print "\n";
    }   

} else {

   function redirect($url) 
   {
    ob_clean();
    header('Location: '.$url);
    ob_end_flush();
    die();
    }
    redirect('login.php');
}
?>    

For some reason the included sub-directory page, when calling the download, will include the main page HTML code when downloading in the dostorted export.XLS file.

Note:

1. I am in the 1st week of learning PHP. I have searched but couldn't find what could have possibly gone wrong.
2. .htaccess makes local access only on /hidden to avoid direct access to the folder without having session set, so include option seems the only secured method to download from the /hidden folder.