Hi. I'm fifteen, and for a while, I've been getting these weird, sharp shooting pains in my chest, and in my sides, just beneath my rib cage. They are painful, and momentarily paralyzing. Sometimes they are random, but they do mostly occur whenever I laugh too hard, breathe in too deeply, or walk long distances. Also, whenever I get up or move too fast, I will get light headed, dizzy and my vision will blank completely. I feel nauseous and need to sit back down quickly. Please help.