I accidentally hid an individual post by someone else (or story as Facebook calls it) on the news feed. The post is now hidden everywhere, even on the page of the poster. The rest of the posts by the same poster are still on my news feed and on the poster's page, and I still 'like' the page. Facebook gave me the option to undo it, but after a simple refresh of the page it disappeared. The post in question was by MacRumors, and I did it again with the MakeUseOf page to test it. I believe you can also do this with posts by your friends. Is there any way to unhide posts? The solution may also be a simple script/tool to fool Facebook so that it shows the undo button to unhide again.
They keep changing how this works. Not sure if this is quite the same as what you describe - as that's never happened to me, but perhaps you might find it appears in the same place??
The latest instruction is - hover your mouse over the News Feed link at the top left and an edit icon will appear to the left of it. You can then click on that to get a list of the people, pages and apps you have hidden and can unhide them.