What you went though with Gidget was a traumatic experience. It is hard enough to lose a beloved pet under any circumstances but what you went though was horrible. I feel you are suffering from a form of Post-traumatic stress disorder (PTSD).
Post-traumatic stress disorder (PTSD): Symptoms - MayoClinic.com
My oldest daughter is suffering from PTSD because of all the brain surgeries she had several years ago and all the horrible things she saw when she was in the hospital. She has finally got professional help and it has helped her a lot.
I don't think you will ever completely get over that tragic day but I pray with time you will do better. Just try to think of the good times you had with Gidget.