why is one interesting and even desirable perhaps, and the other not?
At least as I feel it is, it's not about the pain as such being pleasurable, in itself.
And I'm not into extremely painful things anyway in real life.
A big part is giving myself into that situation (being helpless and knowing there will be pain), not knowing exactly when/where/how, and yielding to that pain and letting it go through me. For that it's important that it's a kind of pain that's mostly something I can still handle ... perhaps for a few moments bringing me to, or beyond the border of that. I've put myself into that situation, only he controls it and can make it stop, (apart from emergency). I think the very different focus of awareness brought by that uncertainty and anticipation is a huge part of it.
The pain of injury or chronic disease doesn't care for me, it's just there, according to its own dumb progression.
However, pain in BDSM is all about caring for me. If that sounds like something that's mad and makes a little sense at the same time it's probably right
I agree with Eul, for me it's essential that it's done by someone who's close. And it definitely has to be done by someone, not just happen - here maybe a silly analogy helps, ... tickling yourself doesn't work that well either
To give an example, there was absolutely nothing in the slightest erotic at having an area of skin sized about two postcards fall off my left hand and arm after serious second degree burns. This was just agonizing pain that had nothing to do with anything going on in my mind - which went quite blank. Although there were some interesting things to learn about pain during the healing process.
In contrast, getting 'tortured' with hot wax while blindfolded pushes my buttons
especially when he uses a knife afterwards to slowly remove the wax, and hint at doing more...
other pains like whipping do stimulate pheromones (I think, or something of the sort), back-pain doesn't - I believe violent taste sensations like hot chillis have a similar effect
Actually capsaicin, the active ingredient in chilis, directly triggers nociceptors and the body responds as if a burn or abrasion had happened; it answers with endorphin release, and also increased circulation and an inflammatory response. (That inflammatory response can cause actual damage if it's extreme... otherwise though capsaicin's effect is a harmless trick on the body's chemistry ... unless a person has been taking certain drugs, in which case things get dangerous)
-- I think it's perfectly probable to assume that people will have somewhat different 'response curves' to such stimuli and so some people will find a 'sweet spot' where a certain amount of 'pain stimulation' gives them the ideal amount of endorphin response.
And for some that might be chili, for others tough sports challenges, for others BDSM. Of course BDSM adds on all the wonderful mindgames mentioned above, which feasting on hot chilis really doesn't have. For 'Tortures' that aren't too severe - milder forms of whipping for instance, that aren't out to destroy tissue - I think it's entirely plausible that depending on who you are, they might mobilize an endorphin response that's out of proportion to the actual physical stress on the tissue. Because the truth is that our body & brain have no way of detecting "destruction" or "damage" happening to the body ... all that can be reacted to is the signals of the receptor systems, that are supposed to warn of it ... and in a way, due to the imperfection of that response ... with BDSM we are perhaps tricking our body and mind to give us pleasures we would not otherwise have.
The high from extreme sports I'd say has a different aspect, as I think it has a lot to do also with exerting discipline and overcoming part of yourself (what we call in German the '
innere Schweinehund ', so that while the athlete in a way tortures herself, she's being master and slave at the same time, mastering and dominating that part of herself that would want to give up, punishing herself with exertion and yes pain, but also rewarding with the high, and the pride of self-mastery. I'm not any kind of supercompetitive or sensationalist athlete but I do absolutely rely when running or swimming longer distances on breaking past that point where everything says 'you've got to stop' and then tapping into a a special state that comes beyond that.
In many injuries or diseases pain will always hugely overwhelm any imaginable counteracting pleasure coming from endorphins... maybe they just manage to round the edges a bit. Then of course there are situations where the body is prepared for an exceptional state (such as childbirth). But taking into account how the human body and perception work, I think it's plausibel that some people might have that 'sweet spot' of pleasure and pain while others perhaps not so much.
I don't readily resort to painkillers, though naturally I want to know what's causing the pain and want it stopped - but it's part of life, I accept it - but I don't know whether that's really anything to do with being a masochist.
No idea; it's true for me that I rather tend to absorb pain too well, and sometimes should have had it looked into earlier; also in situations I've been prescribed painkillers and tried them, my experience has been that they didn't seem to make too much of a difference; it's seemed to me more effective to learn to deal with the pain.