AEM, I'm 36, and until now Ive never been diagnosed with anything, but anxiety disorder. So I can't really relate to what your feeling, but can with palpitaions.
I started getting a mild left upper back thoracic cramp after lifting heavy weights last year and a few months later started getting the same back cramps along with cramp like sensation under my left breast and left cleavage area during anxiety attacks.
Ive had EKGs, iodine scan of my heart and echos and nothing has been been found so far. Docs tell me it's my constant worring that causes my muscles to tense up, which in turn give me pain and then I freak out thinking I'm having a heart attack and get palpitations and dizziness from the shallow breathing which gives me a panic attack, that have sent me to the ER with high blood pressure (190/9

, which then subsides after I've calmed down.
Those with anxiety should read the below web page re BEATING ANXIETY AND PHOBIAS, it's advices have helped me a lot to control my anxieties symptoms, along with taking 250 mg of magnesium pills twice a day. I too have felt my hr pulse at night when I'm laying in bed and keeping hydrated has helped me not feel that feeling as much, anymore. You should try it. Also try to do so yoga or breathing meditations to aid you with the anxiety symtomps. Hope it helps