Three weeks ago I experienced sudden pressure and pain, accompanied by difficulty breathing, in my mid- to upper back, left side. Normal breathing returned in a few minutes, and the pain/pressure gradually diminished over an hour or so. Since then I have had several similar episodes (one so bad that I was terrified), and all occur when my back is pressing against something like the floor (turning from one side to the other while lying down, for example) or back pressing against pillows while seated on bed. Very scary for me.