@adams52– A warm welcome to Connect. I'm glad you shared your history and I'm sorry that you are having these difficult symptoms. Panic attacks can be very frightening. One of the symptoms that I experience when I'm very stressed is disassociation too.
First shortness of breath is a classic symptom of smoking. We are not doctors so I can't diagnosis you. From my own experiences it sounds as if your symptoms are stress related, they come and then go after your exam is taken. I use to dry heaves before mine!
Your back and other aches should be looked at by a doctor if they don't subside. But when you are tense you can really feel your whole body ache.
I hope this helps. How did you do on your exams?