query_posts in sidebar for post category

try to change your line into:

global $post;
$args = array(
  'posts_per_page' => 5, //limit the post numbers,or use -1 for all
  'post__not_in' => array($post->ID), //exclude current post
  'category__in' =>  wp_get_post_categories( $post->ID ) //use categories of current post
);
query_posts( $args );

https://codex.www.ads-software.com/Class_Reference/WP_Query#Parameters
https://codex.www.ads-software.com/Function_Reference/wp_get_post_categories

and add a wp_reset_query(); after the endif; or endwhile; of this loop.

generally, it would be better if you could use WP_Query() for a secondary loop such as your example.
https://codex.www.ads-software.com/Class_Reference/WP_Query

Wow! Thanks!! That worked great ??

Is it possible to display posts from a certain category AND with a certain tag? It doesn’t seem to work expanding your code like this:

global $post;
$args = array(
  'posts_per_page' => 5, //limit the post numbers,or use -1 for all
  'post__not_in' => array($post->ID), //exclude current post
  'category__in' =>  wp_get_post_categories( $post->ID ), //use categories of current post
  'tag__in' =>  wp_get_post_tags( $post->ID ) //use tags of current post?
);
query_posts( $args );

slight complication:

https://codex.www.ads-software.com/Function_Reference/wp_get_post_tags

as you can see, the default output of this function is different from the one of ‘wp-get-post-categories()

needs to be corrected by the proper use of the $args array:
https://codex.www.ads-software.com/Function_Reference/wp_get_object_terms#Argument_Options

i.e.:

'tag__in' => wp_get_post_tags( $post->ID, array( 'fields' => 'ids') ) //use tags of current post

the result is a ‘OR’ -> the related posts will be from any of the categories or any of the tags.