I went swimming, 5 minutes, top. And I was fine, I took a nap and then went to work. At work, I felt a pain in the middle of my chest, like a knife being there after 10 minutes the acute pain went away, leaving only a slight discomfort. Now, I noticed it happens every time I go to the water. After 4-5 hours that i leave the water, the pain is there. I don't know what it is if I lean my shoulders in, the pain is even bigger. Now, I just don't go to the water. I workout at the gym with heavy weights and never felt something like this. What do you guys think it is?