I have been having pains across my upper back on the left side and it goes across the chest and down my arm and pains real bad then goes away. My blood pressure is normal I think . I am on blood pressure medicine .So when it happens and not often and I do have breast cyst on that side under my arm that when Examined hurt . Could it be from that ? It takes a bit for me to even move my left arm from the pain even across the back part under the arm .Not all the time only if I move my arm a certain way then the attack comes on any info would help.
The kind of pain you have is similar to mine when I've having problems with a rotator cuff tear. But I know from an MRI that's what it is.
It's not wise to try to diagnose these kinds of pain via an online forum.
The kind of pain you describe is as Maggie suggests - possibly a heart attack symptom. You need to see a medical professional or go directly to the ER.