title: session id value changes
body: <p>I am writing a PHP website. I have a <code>$_SESSION['id']</code> that hold the username id of a user, which I will use this value later on in my scripting. However, I notice that the ID changes as I surf the site.</p>
  
  <p>Is <code>id</code> reserved in any way? Or, should I change <code>id</code> to something else?</p>
  
  <p>This problem is happening whenever I click on a button several times. I am 100% sure that I'm not altering <code>$_SESSION['id']</code> beyond the initial login.</p>
  
  <p>Could someone please help me understand what is happening, and how it can be fixed.</p>