It is curious if it was merely the endorphins released that causes me to have these feelings that I never experienced it before we started our taken in hand relationship. We had tried erotic spanking before and it did very little for us and left us with virtually no emotional effect at all. It certainly is more than a reaction to pure pain. It hits me on a much deeper emotional level than anything I experience during erotic spanking. Sometimes erotic spanking can actually be more severe than a discipline spanking. We play a lot more than we discipline and I only get the intense feelings like I described during more serious spankings. Sometimes I get some of those feeling without being spanked at all. I once got those feeling simply laying over my husbands lap. That feeling of helplessness and loss of control washed over me and brought me to tears before he even laid a hand on me. I felt the pure acceptance I do feel normally after a spanking without any spanking at all.
Perhaps the reason the two punishment spankings did not do this for you was because you are not wired for authority based relationships in the same way I am. It could also be that the person giving the spanking was not able to read you well enough to know when you reached that place of acceptance. For me to get there I first have to go through a phase where I feel complete panic and helplessness. I am sure it is different for everyone. I only really know my own experiences, although other people have described very similar experiences to mine and Diamond's to me many times.
I think it is more than just a release of endorphins, although I do not doubt that endorphins are released and that they do feel very nice. Or perhaps the way endorphins are released in my brain is dependant on my relationship structure. Who knows the brain is a very complicated thing and I do not pretend to understand it.