Kink or fetish BDSM - This is the form where people, occasionally, seek to use power elements, predominantly for their sexual pleasure, without turning it into a lifestyle.
Is BDSM abnormal?
There are power elements in all forms of human behavior: at work, at home, in politics, in sports and in (sexual) relationships. Magnifying the power element in your relationship is not abnormal. The current opinion among professionals (laid down in various diagnostic manuals, such as the American Diagnostic and Statistical Manual) is that consensual power exchange between informed and well-adjusted adults is normal and harmless (sexual) behavior.
Why are many people so secretive about their BDSM emotions?
Regardless the subject: it is not easy to have to tell the world you are "different". This is true for everyone, who nurtures emotions, feelings or ideals that do not coinside with their social environment. People, brought up in a business-environment, will often have a hard time telling their parents and friends they'd rather be a painter or an actress, for example. Gay people face a similar problem and so do democrats who came from a traditonal republican nest. The phenomena is known as "coming out (of the closet)" (telling your environment you are different) and that is a difficult process that requires a lot of juggling between defending and explaining yourself to a probably unwilling audience People with a BDSM-inclination face the same problem. Quite often this even leads to a situation where people - regretfully - are too scared to even tell their partner about their emotions.