All contacts gone allthough nothing done

Hey there,

I was sitting during lunch looking at my iPhone 4S and seeing that it gave me the loading circle (the one before it shots down).

Even the loading circle was not moving properly.

I re-booted the phone and had to realize that all contact were gone all of the sudden.

All the call and missed calls are still there. Even the messages, pictures etc. still there.

The only effected area is the contact book.

I haven't done any sync for the last few weeks as I have bought a new MacBook Pro.

Can anyone advise what to do to get the contacts back?

Thank you for your help.