I never ever use http://wordpress.com/#!/post/ on the main page of WordPress.com because it creates Asides and Asides are post formats. They don't have Titles and can't have Categories assigned to them.

Aside – These are brief snippets of text that aren’t quite whole blog posts. Useful for quick thoughts and anecdotes http://en.support.wordpress.com/posts/post-formats/

You ought to be able to go here > Dashboard > All Posts > Posts and locate the post. If it's not there then look in your Drafts. Edit the post and add your video to it and even change the post format to a Standard post format.
http://en.support.wordpress.com/posts/edit-posts-screen/

Standard – Your normal, average, everyday blog post. This is the default styling for your theme.

If that's what's happened then in the future only create Posts in your own blog's dashboard here > http://imageguy.wordpress.com/post-new.php