Strange behavior on my iphone

Hello,

I have iPhone 4s....I am not sure when it really happens though...
This is the second time just happened to my iphone...
My all contacts have been deleted for some reason...

I kinda remember this happening at the very first time..
I was charging my phone to my car....then...after that, my all contacts have been deleted..I don't believe charging phone to the car causes the deletion of my all contacts on iPhone, but as far as I remember, this is happened...

Couple of days ago..again, my all contacts have been deleted for some reasons...not sure about this incident..I remember I've charged my phone to the car..but not sure this is just happened right after that or not like the first time....

It is really strange..why I see this strange behavior?
Anybody has same exp?

Thanks,