It sounds like a facebook phishing scam. DO NOT OPEN E-Mail ( Just delete it ).
They send this out in hopes that you will click on the link in the e-mail and unknowingly logon to their fake facebook server and then a hacker quickly uses this information at the real facebook site and takes ownership of your account and with this control can then spam others on friends list with anything they chose to do so as well as any sites that have facebook passthrough authentication they also would have the ability to access and steal information etc or hold it for ransom with a monetary demand to give you it back.
Some facebook accounts that I have heard compromised in the past have even had false damaging information posted such as stating that the person is coming out of the closet, starting fights with friends posting hateful information, etc and far worse.