Re: Constant shortness of Breath!!
This is the same problem I have. I have also had a plethora of tests, albeit not the extent you have, though.
Anyways, it's psychological because you're aware of your breathing. 99% of people breathe naturally, as it's a natural event that your body performs; however, for some of us, something triggers something within our minds to be self-aware of our breathing, so it's like we have to tell our bodies to breathe sufficiently.
Mine happened spontaneously, too, and put me in a full-fledged panic attack. I went to the ER where they determined my oxygen level at my fingertips was 98% (excellent). I then had an EKG done and blood work and lung function test - all came back fine. During exercise it rarely happens nor does it get worse, and my doctor said that makes it only one thing - anxiety.
It does not occur when sleeping or when I'm watching TV or a movie, or doing activities. It occurs when I'm just sitting around and then I think about it and voilą, I need to take a deep breathe.
As hard as it is to understand, you need to try to focus on other things. Like you, I've had this for YEARS (about 3), and it has gone away for MONTHS at a time, only to rear its ugly head again. It seems to happen more when I just have idle time (i.e. when it's very cold out and I'm inside doing a whole lot of nothing!).
Hang in there!