Facebook has changed your settings and said nothing (again). Take a look at your URL (top box on your Facebook screen.) If you see "http" or just "www" instead of "https" you DO NOT have a secure session and can be Hacked.
To remedy go to "Account Settings"
Click "Security" on the left top corner.
Click "Edit" next to "Secure Browsing" Check box.
Facebook has automatically set it on the non-secure setting! Do everyone a huge favour and spread the word.