I have a couple of friends who identify as subs in their relationship and when they play with their Dom(me)s they both describe subspace as a state of euphoria for them. They consider it a huge release of stress to let go and succumb to the play. This is only healthy if there is good aftercare for the subs. They often need to have a few hours of cuddling and stroking and sleeping in the arms of their partners after, but they consider the whole thing very healing for them. I know that for myself, that kind of power exchange wouldn't work for me, but it seems to work very well for them.
I don't identify as a sub but I have been a bottom for some BDSM play. I enjoy the challenge and stretching of my sensory experience that such play brings. It's also true that you actually experience a rush of endorphins with that kind of play if the person topping you is doing it well and paying attention.