This one is kind of major...

I added a data entry in the admin area and later decided I did not need it, so I deleted it. When I did this for some reason it removed ALL data entries in the Admin area!

I was able to go back into the database through phpMyAdmin and found that it had only deleted all the parent entries (Countries, US States, etc.) and all the other keys were still there. I fixed this by adding the data entries back in the admin area, then correcting the ID in the database through phpMyAdmin to what it was originally and everything came back.

If this happens to anybody don't panic (like I did initially!), it's not too difficult to fix, but there is a bug somewhere in the Admin area that must have caused this.