get_the_category() won't change between category requests

I have searched all over and can’t seem to find any help or docs on why get_the_category doesn’t change between category requests.

Basically what I’m trying to do is have a custom sidebar display on certain categories.
In category.php I have:

$category = get_the_category();
$category_slug = $category[0]->slug;

and

if ( in_array($category_slug, $pdi_cats) ) {

	?>
    <div id="sidebar-container" class="cat-sidebar-<?php echo $category_slug; ?>">

	<?php
	if ( !function_exists('dynamic_sidebar') || !dynamic_sidebar( $category_slug . '-sidebar' ) ) {

	}
	?>

	</div><!--sidebar-container-->
	<?php

} else {

	get_sidebar();

}

which loops through my array of custom categories and if the current category is one of them displays that sidebar.

The problem is that $category_slug won’t change when I change categories. It keeps displaying the first category that I pulled up like it’s caching it. Am I totally missing something here?