These are different ways of expressing that you are Worried.
Informal: I'm worried about my dog.
Formal: I can't help thinking about the economic situation.
Informal
I'm worried about...
British
American
I'm afraid...
British
American
I'm really nervous.
British
American
I'm scared that...
British
American
I'm so worried.
British
American
Formal
I can't help thinking...
British
American
I've been worried sick about...
British
American
I can't stop thinking about it.
British
American
It's been keeping me awake at night.
British
American
I've got butterflies in my stomach.
British
American
