I guess different subs experience submission in a different way.
While some want to be physically dominated and get turned on by a forceful hand and a spanking, others may want to be blackmailed in obeying to do (humiliating) things for their Dom(me), and yet others are arroused just by the thought and act of pleasuring their Dominant and don't need a physical approach at all.
So pain and restraints are definitely not necessary, whatever works for you. I think it is the same for Dom(me)s, some like to take a physical approach, while others enjoy an obedient submissive.

I think eventually the sensation comes mostly from the mind. Some people need more physical acts to stimulate their mind, while others can get off easily by just fantasizing or watching. It's the same for subs and Dom(me)s.