Hello Welcome to HealthcareMagic! The symptoms that you describe is more suggestive of pericarditis. It is inflammation of the sac surrounding your heart which commonly presents with sharp chest pain that usually comes quickly. Variety of factors may cause pericarditis such as infection, trauma, certain drugs etc. The pain is located mostly on the left side (or behind the breastbone). Pain is relieved by sitting up and leaning forward and worsened while lying down and deep breathing. The diagnosis is confirmed with EKG and Echo-cardiography. The other possible condition that causes chest pain with deep breathing and lying down is pleurisy (pleuritis). It is inflammation of the lining of the lungs. If the inflammation on the left side the pain may locate in the area around the heart. To confirm the diagnosis your doctor may prescribe x-ray or CT scan according to the initial physical exam findings. I hope the above information will be helpful for you. Please, feel free to ask me if there is anything else you need to know. Thank you, Malik Amonov MD