Error 504 Gateway Timeout when logging into /wp-admin

This morning while attempting to post, I kept getting that “Connection lost” message, indicating that the post was being backed up to my browser just in case. I waited for over an hour for it to, you know, right itself. No luck. My connection is fine and has been fine all morning. I’m able to browse the web and pull up other pages (even my client’s WP admin pages – and I can save w/o the connection lost message).

I was able to update to WP 4.0 (after multiple attempts) but I’m still getting the Error 504 at *myblog*/wp-admin/edit.php.

What’s going on?