Session not retaining original value on next page - php

Question

This page shows the status of several chatrooms. A user can click a button to get them into the room of the person they choose. The nickname session of the person they select should be sent to the room through the form. The sessions are correct on this page, but when the values are submitted to the room, the nickname changes to the 1st nickname in the database, rather than the one I have passed to the page. How can I get the session to use the data it initially collected? (The page that receives the values only echos sessions, so I didn't post it)
<?php
session_start();
require_once('connect.php');
$con = mysqli_connect(DBHOST, DBUSER, DBPASS, DBNAME) or die('Connection failed: ' . mysqli_connect_error());
$sql = mysqli_query($con, "SELECT UserType, NickName, Online, InChat FROM main_member WHERE UserType = 2 ORDER BY Online DESC");
while($row = mysqli_fetch_array($sql)){
$UserType = $row['UserType'];
$NickName = $row['NickName'];
$Online = $row['Online'];
$InChat = $row['InChat'];
$_SESSION['NickName_Session'] = $NickName;
echo '<table width="353" border="0">';
echo '<tbody>';
echo '<tr>';
echo '<td width="248" height="51">';
echo Status($Online,$InChat,$NickName);
echo '</td>';
echo '</tr>';
echo '</tbody>';
echo '</table>';
}
function Status($Online,$InChat,$NickName){
if ($Online == 0) {
echo 'I am not online.';
}
elseif($Online == 1 && $InChat == 0){
echo 'I am online and I will be in my chatroom shortly.';
}
elseif($Online == 1 && $InChat == 1){
echo 'I am online.';
echo '<form name="get_nickname" id="get_nickname" action="script.php" method="POST">';
echo '<input type="hidden" name="nickname" id="nickname" value="' . $_SESSION['NickName_Session'] . '">';
echo '<input type="submit" name="submit" id="submit" value="Start Chat" />';
echo '</form>';
}
}
mysqli_close($con);
?>
this is the script page:
session_start();
if(!isset($_SESSION['file'])) {
$_SESSION['file'] = (rand(1000000, 9999999)) . round(10*microtime(TRUE));
}
if(isset($_POST['create'])) {
$_SESSION['file'] = (rand(1000000, 9999999)) . round(10*microtime(TRUE));
}
$url='chat_container.php';
Header("Location: $url");
exit();
and here is the chat container where I need the nickname:
session_start();
require_once('connect.php');
echo $_SESSION['NickName_Session'];