I don't think it's at all unusual to feel like you are "falling apart" after the treatment has stopped. Your body and mind are just exhausted, you don't feel that you are actively fighting the cancer and you see your Drs less so you can't express your fears as much.
If you are really worried about something, you should call your Dr before your appt and express your concerns. If your anxiety stays elevated, you should also consider talking to someone.
But keep in mind, this is some experience you have just been through and being scared and emotional is so understandable.
My husband also developed a cough. It was part seasonal allergies and part of that thick mucous stuff. He found mucinex helped. Maybe you have some version of something like that that you can try.