iPhone 4 Contacts Disappeared After Receiving Text Message

This morning when I woke up to a text message it showed the full name. Literally just about an hour later I received another message from the same person, but it only showed the phone number. When I went into the Contacts I saw it was completely empty. All of my favorites and recent calls are there but they're just the phone numbers, no names or anything else. How did this happen? I didn't change anything and I have no idea what to do.