I have had this same "symptom" since I was around 17 years old(24 right now). I went to several doctors in regards to this fearing I had some odd ailment and was going to die from it. This is the basics of what the doc told me about this, not sure if its correct though as I have been told several different things. This explanation just made the most sense to me. He told me it wasnt my heart due to the pains being in the left side of my chest, he told me if it were to be my heart I would feel the pains more towards the center rather than the right or left side. Apparently somewhere down in your stomach area there is a nerve center that extends upwards from around your sternum area to 3/4 of the way up your chest possibly further. So what your basically feeling is some kind of acid reflux bullshit that is agitating that nerve which in turn sends out the sensations of pain wahtever they may be. I personally feel it different ways, sometimes it feel like a lightning strike of stabbing pain other time it feels like someone is pouring acid into my left lung. Fortunately it never lasts much longer than 30 minutes a stretch but it is annoying as hell. Hope this helps some of you out.