Since Sunday, I have been getting weird electric shock type pains running from under my left breast around to the underside of my left arm . It happens mostly when I run or do something high impact. Occasionally it happens when I sit up in bed or when I am asleep and roll over it will happen, which wakes me up. It usually subsides within a few seconds but it s really painful in the meantime and I have to stop whatever I am doing. What could be causing this? I m 30 and fairly active but also overweight . I don t have anxiety issues or any other big medical problems. I ve had a history of tendinitis but that was all in my feet. I don t really want to go to the dr because I just don t have the time.