Some of the old school peeps that trained me often said sub space is something one could only achieve if at all during super high intensity painful sessions and that it was a rare almost sacred occurrence.
In my own experience I have come to recognize several different varieties and levels of it.
Sometimes I hit a version of it and no one has so much as even laid a finger on me.
The main way I’ve managed to slide into it or something like it is usually through a combination of humiliation, intense duration positional Shibari induced muscle tension and orgasm on command.
I also suppose however similar it may be for everyone that experiences it, that in fact its actually also unique for each one, heck sometimes the "sub space" place for me isn’t even always the same sensation, some times its not even always a good place for me to be in; especially if I drop later.
Sometimes it makes me feel euphoria, intense longing, out of body almost dreaming ,floating, powerful, consumed, weak, strong, alive, dead, terrified like holding an electrical fence, like drowning, like breathing air for the first time, like what freedom, true freedom tastes like.