Periodically, when sitting for a while, I get an electric shock sensation behind my upper-left shoulder blade. It feels like when the dentist hits a nerve when administering a numbing shot. I can go for weeks without experiencing this and then it just happens when I am sitting reading or watching tv. It goes away by itself and my pulse feels normal and I have no difficulty breathing. I am currently taking no prescription medications, I just take vitamins and low-dose aspirin. I have been rear-ended several times and slipped on ice and landed on my right shoulder and I heard bones in my chest knock together with a sharp rap. Is it possible skeletal elements are mis-aligned and pressing on thoracic nerves.