Break down

Hi all - something happened to me this weekend. I feel as if my heart is going to jump out of my chest. My chest feels tight and I have a headache. I can't sleep and I feel faint. When I am focused on the kids or doing something I am fine. As soon as I am alone or trying to go to sleep this comes over me. Could this be a mental breakdown? It has been a little over a year since diagnosis and I have never felt like this before. I think that sometimes I try too hard to hold all of this in and now...I don't know. Am I losing it?
This past Friday a play that I had helped write was in another production. It has a lot to do with my initial diagnosis, chemotherapy and personal fear dealing with the cancer. I didn't really want to go but felt I had to since there was a new girl playing me. Well, I wanted to run away. I didn't want to be there at all. Then I have felt just awful - weird. Anyone else out there have this happen to them? I'm also getting extremely close to my last Herceptin treatment. Maybe this is also doing it to me? Thanks - Ruth