Not for the faint of heart.
I just finished watching Secretary, directed by Steven Shainberg by, starring Maggie Gyllenhaal. Winner of a Sundance along with many other awards.
What a super intense movie. It really deals with the individual experience of a couple negotiating the realm of BDSM.
Interesting reading if you want to get a little bit more true life information: The Way of Whips and Chains: BDSM as a life path. by a woman named Sasha. Discussing BDSM as her own religious form of transcention and healing at the same time.
I've always been super interested in people who are really into this stuff. Some people take it so far that it seems to go against all evolutionary instinct altogether.
A lot of artists move into this realm as well, dealing with the breaking down or mangling of the body. One of my favorite all time artists, Belinde De Bruyckere, working with the intensity of destroying and recreating the human form.
Last but not least: A friend posted this song and I listened to it right after watching this movie. I found the mood very appropriate.