I have a condition in my chest called "tse tse syndrome" but the technical name is intrachostal chondritis. It can mimic a heart attack and has with me a good many times. It's inflammation of the soft tissue in and around the ribs. Very, very unpleasant. It's always there but when it's especially bad, I find that slouching with my posture will often set it off and just lying down or sitting up straight will ease it. It also seems to be affecting the tissues in my right shoulder where I also have a severe tendonitis.