$.ajax({
   url: '/update-session.php',
   data: {"x":e.pageX,"y":e.pageY},
   type: 'post',
   success:function(data){
       // if you care. 
   }
});

update-session.php:

update-session.php:

$_SESSION['pageX'] = $_POST['x'];
$_SESSION['pageY'] = $_POST['y'];

http://api.jquery.com/jQuery.ajax/