It is part of both.
My general personality is partly submissive, deferring to others and working toward some kind of harmony. I consider myself a good follower: once someone has established authority, I will recognize it as long as I consider it legitimate; should I start considering it as being illegitimate, I will usually try to remove myself from the situation rather than overthrow the authority in question. I (partly cowardly) show my disapproval by my increasing and eventually complete absence.
In addition to my follower quirks, I also prefer a harmonious state where everyone's wishes (including my own) are fulfilled. For a long time (and still to an extent) I've focused more on the joys of others than those of my own.
In recent years though, I've increasingly rebelled against this part of me. Submitting myself to others doesn't necessarily achieve what I want and way too often leaves me short. My assertiveness is growing and it feels good.
Currently, submission plays a significant role in my sexuality. Until I find the confidence in myself to lead, I want to be led. I am attracted to decisiveness and clarity, as well as caring, but authoritative sexual partners.
In terms of sexual fantasy, my limits expand to include a lot more dictatorial sex where I feed off of both the dominant dictator and the submissive subject.