I have received this error a while ago, Facebook might be experiencing server overload or some unexpected errors. It should be back in a minute or two. All you can do now is wait patiently.
What to do? Nothing, might be a good time to do something else and if after sometime and you”re still getting Facebook Account Temporarily Unavailable, try using other browser or ask your friends if they can open their profile and if they do, try clearing your browsers cookies and cache.