Wow. This is deep. Now, before I get all philosophical and shit, allow me to define "subspace" for those who are not BDSM or new-age savvy. Subspace is a trance-like state of mind. This particular state can vary from moderate to very intense, and it's usually experienced by weird religious folk, some bizarre cultists, sportsmen, drug meddlers, Hindu Gods, and those who are into hardcore D/s sessions.
Now let's get back to this wonderful letter. A couple of weeks ago I did write that the dungeon is a place for suffering and humiliation, not therapy. And weeks later, I still stand by my words. The dungeon is not a shrink's office. I know what you're trying to say Curious Bottom. It is very possible for sadomasochistic activities to lead to transcendent experiences, and in order for that to happen BDSM doesn't have to be therapeutic, and insecurities have little to do with it.
Subspace, as you call it, is nothing but a mere chemical reaction in your brain -- a rush of adrenaline in your body, release of dopamine in your pituitary gland, and endorphins and oxytocin in your brain. Basically it's like a chain of erratic fireworks happening in your body. Any human being on this planet can experience it.
I've been in that transcendent state many times, and it's not necessarily restricted to my intense BDSM sessions. Anything that gives me pleasure -- from sex to long distance swimming -- can send me into that trance-like frenzy. Hardcore runners get to experience it quite often. You call it subspace and they call it the runner's high. A feeling of euphoria. The pain subsides and your body goes numb. You're out of breath, but keep on moving. You lose it all and suddenly pain turns into pleasure.
Subspace is real. And I am sure you can experience it if you find the right playmate.