question: When cycling after about 20 mins or so I feel a fluttering feeling in my upper area just below my left side under my collar bone rib area. It feels like I need to take a big breath of air and adrenaline races around my body. I feel like I need to stop and get myself together. I m 32, and with possible ( not diagnosed yet) costochondritis. It makes me nervous to excersise to my full potential an I m afraid it might be my heart.