Hi Abidaisi,
This is a good question and an important thing to try and nail down.
When I think of my "shortness of breath", it's defining feature is that (even though I am at rest) I take a normal breath in but it doesn't feel like I have had "enough". I then try for a bigger breath. Sometimes this will "click over" my breathing - give me the feeling that my need for air has been satisfied and i can breathe out, but, sometimes, even a bigger breath can't satisfy the feeling of having 'enough". The drive to breathe is the most basic conscious drive we have. It kicks in the moment we are born (and we are even practicing in the womb before we are born) so when our alarm system tells us we are not getting a big enough breath it is pretty distressing.
I believe this is the moment lots of people with this condition get panicked and then get labelled with a primary panic or anxiety disorder.(I am not arguing that anxiety plays no part in the abnormal breathing patterns of some people, rather that I believe it is NOT the answer for all of them).
For me, when I get to this point I just feel resigned ("here it goes again") and I resort to the other "tricks" I have to try and get a satisfying breathe: wriggling my jaw to start a yawn is my usual first trial. Then I try sitting quietly and letting the feeling of suffocation build while telling myself I have been here many times before and I always come through it. It's a faulty alarm and despite its noise I know my oxygen level is ok. Often this leads eventually to an almost unstoppable large gasp which "clicks over" my breathing again. Occasionally I will lie down if I am standing - but always on my side not my back (because I have this belief that the problem has something to do with low blood pressure within my lung blood vessels). Sometimes I will just jump on the spot to trigger a deeper breathe through exercise.
I'm sorry this is so long winded but for me, the term "shortness of breath" doesn't capture the specifics of what I experience.
But the thing is, instantaneously when my breath "clicks over" relief floods through me and I have NO shortness of breath -maybe for minutes, maybe for hours, until the signal to take a deeper breath becomes evident again and I again feel a building "shortness of breath".
All in all, I have (usually) days to weeks where my breathing goes "off", as I have described above, coupled with periods when I can go for months with no problems at all - I have months where my breathing is essentially normal. Maybe the odd unsatisfying breath that is fixed with a bigger "gasp".
I suppose the key feature for me is the complete relief of any sense of "shortness of breath" the instant I click my breathing over.
Hope this is of some help.
Please if you do have shortness of breath though, don't assume it is this until you have been checked out by your doctor. And if you still don't think it is this, and you feel unwell, seek another medical opinion.
Warm regards (it's getting cold on this side of the world!!)