You can give the hidden panel a whirl just by clicking on the more link in the top right hand corner of the demo. When you do this you will see the secret panel is more like an extra layer that sits on top of the page rather than sliding into it. Here is an image of what the hidden panel looks like:
As you can see the secret panel looks like another page on your website. To close the panel just click the more button again and the page will be reverted to its previous state.
In order to get the hidden panel to display all you need to do is make sure that a module is published to the cPanel position in the Joomla module administrator - if you've done this then the template will do the rest. The beauty with this effect is that we have done all the heavy lifting in just a few lines of code - so you get the benefit of a lightbox type overlay but with a smaller page load.
A common issue with hidden panels is that there will be a brief flash of unstyled content (fouc) before the page loads. Vision2 includes a nifty technique to prevent this from ocurring so the secret panel will remain secret or hidden until the user clicks on the more button.