We now return you to your regularly scheduled thread...
For me, the discomfort of the position (Back when I could assume it) was part of it. Now, I have a bad back, so getting comfortable is a pretty important part of getting sexy.
Loss of control, discomfort-pain, humiliation, or just seeing what you can endure can all be part of BDSM, that's why there's so many letters. Some masochists like to be comfortable when you drip hot wax on them too.
Different strokes for different folks.
PS: Auto-philatio is way out of Normal. It's not a tanget, it's roughly Skew. A tangent is comparing the anatomical geometry of attempting Auto-cunnilingus.
If I wanted to strike a Chord, I would have mentioned the Oroborus.