I noticed lately I accidently suck my stomach in most of the time, and when I sit or stand up straight with my stomach relaxed it hurts, especially when I breathe. When I breathe in like that is causes a sharp pain to go from the center of my diaphragm up to the middle of my chest. Is it just because the muscles around my stomach have tightened up? Or could it be something else? Also, I did slip and fall backwards on a hill a few weeks ago, and landed with my hands extended backwards with most of my weight landing on them. It ended up hurting my chest and spine/shoulders really badly, but I thought it was feeling better. (I went to the doctor, got an x-ray done on my ribs and he said I was fine and I probably just hurt some muscles) Could the muscles just not be fully healed yet and causing the pain?