Unfortunately, I have experienced what you are talking about as well. I had a scare for a few months where I thought I had angina or some sort of heart disease that would kill me very soon. For weeks, I was too scared to even walk around a lot, afraid that I would trigger something that my heart couldn't handle. I was eventually diagnosed with costochondritis or simply anxiety..Its kind of true when people say they just diagnose someone with costochondritis just to give them something, but they only do so when they've basically dismissed everything else.
At the moment, what are you worrying about having? I had the exact same symptoms as you once again and had to go to 4 doctors and a well known cardiologist as well as have 3 ecgs and a chest x ray to eventually put my mind at rest.
What you are describing is honestly some of the most common anxiety symptoms...and I managed to put myself into a frenzy of those two nights ago while worrying for ovarian cancer, tricking myself into thinking it had spread to my lungs. When you keep trying to breathe so heavy and take deep breaths, you're putting a strain on your lungs. Its could also cause headaches and dizzyness because you arent letting your body breathe properly, how its meant to. When I keep thinking I can't breathe, I take extremely heavy breathes over and over again to the point where I make my chest sore.
The nausea could also be attributed to simply being scared about all of it...this was one that has hit me even before my hypochondria flared up.
I hope you get better soon. And a d-dimer test is very accurate, so I really would try not to worry too much about it but as I've said, I've been exactly where you are before.
Here I am, still alive, but still worrying that this is the time I am finally right about my disease and I am dying.