Not that I am an expert on this thing, and probably have only experienced one single moment of sub space so far, from what I gather subspace can be attained differently for each individual.

Subs who are into pain, experience sub space through intense pain play. Subs who are into bondage experience sub space through intricate bondage positions, ect.... you get the idea.

I am into humiliation and degradation, and definately not into pain. A little bit maybe, but the majority of the time the pain is not supposed to be pleasurable for me, so I cannot get into any real head space, even when I am being verbally humiliated the whole time.
There was one time though, where I reached that sub space through some intense humiliation and by then pain was not an issue, I could recieve it without being affected by it.

So to sum up my rambling, I wouldn't say that only sub space can be achieved by intense pain. It can be achieved through whatever the sub enjoys. I wouldn't call it any other name, because then you would have to come up with a name for mine.