Your observations are interesting and complex in my case, Rogue. The only pain I enjoy is getting buttock injections from beautiful nurses but it is intense - the more the shots hurt, the greater my thrill - even though I have no fetish about other posterior pain, such as spanking.
My adrenalin rush begins when I make the appointment and increases until I feel about to burst with anxiety by the time she tells me to pull down pants and bend over. When I don't have a medical need for injections I sometimes go to a dominatrix nurse, where I wallow the humiliating form of restraint I so dreaded in my youth - being held across the receptionist's lap.
With regard to satisfaction about giving the nurse pleasure, I once asked if she enjoyed injecting my bottom and she replied, "We're not supposed to admit it" whilst receptionists freely admit that they enjoy watching me get shots back there. I am always excited at the thought of their pleasure but scared when waiting in position at the dominatrix because I know it is her job to make the injections as painful as possible.
I am unfortunately never as genuinely frightened as I was about getting real shots like that in my youth, and particularly adolescence, so I sometimes try to argue with the "nurse" about the injection site for the purpose of making her strict (which she always is) with the result that the receptionist often has to "help me" drop trousers and pull down pants before I bend over her lap. Waiting in that vulnerable position while the receptionist sensually strokes my bare bottom and utters such condescending remarks as, "You know you have to get them; there's nothing you can do about it now," and the dominatrix warning, "Don't worry if you can't sit down for a few days after getting these; it is a normal reaction," increases my apprehension to an incredible level.
Whilst pleasurable pain is the subject of this section, I agree that anticipation is hormonal and the added thrill of embarrassment when I get buttock injections confirms the theory of excitement at giving others pleasure about my pain.