Like someone else said, you're sexually submissve, not necessarily a sexual masochist. Although someone who is sexually submissive isn't always a masochist, but people who are masochistic usually are submissive. I think I phrased that right... Someone can submit to his or her partner without being hurt or made to suffer.
In my case, I prefer the submissive role in a sexual relationship. I do enjoy the infliction of pain. Whether that makes me a sexual masochist or not doesn't really matter to me because I know what I prefer sexually.
Receiving moderate to severe amounts of pain is an endorphin rush for me. I'm going to spare all of you the details because I don't feel it would be appropriate for this site. After being in a 10-month 24-7 power-exchange dominant/submissive relationship, I have been well accustomed to daily beatings etc. But afterwards, I feel more centered, and more in control of things... a natrual high if you will.
It boils down to preference. If that's what you prefer, run with it!
-Nayana