Having experienced pain inside and outside of BDSM I can tell you it is a completely different experience. I have found that pain from a spanking or even a whipping given knowing that you earned it and your Master loves you enough to punish you can be very erotic and the pain can be a stimulant even if you don't enjoy pain.

Of course these days I am a bit of a pain slut, and my Master can vouch for that, but it is more the situation than the pain itself that I enjoy