I've been having this weird pain and heaviness in my lower chest whenever Im alone, like when Im outside by myself or just at home. It starts after a while, and then I get this mild shortness of breath, and my pulse goes up to like 105. I had an X-ray, CT pulmonary angiogram, ECG, and 2D echo, but they all came back normal. Also, when I lie down, my feet feel really heavy. Any idea what's going on?