Everyone has limits, even doms have them. There are lines they just don't feel comfortable crossing. Some Doms just aren't comfortable with inflicting pain, but are ok with spanking on occasion with a willing partner. There are many other limits they might have. Much ado is made about submissive limits, we have categories, hard limits, soft limits...this limit...that.
Some feel that slaves shouldn't have any limits. But this mouse thinks that everyone has something they just don't feel comfortable with. When that limit is pushed for whatever reason it can cause great anxiety, because it can be counter to everything she believes and holds dear. It keeps her from being pleasing. It makes her feel insecure. It can cause lots of different emotions and fears to bubble to the surface.
What is done about those feelings is up to the Dom:
He can stay the course but allow his slave a chance to catch up to where he is, pausing to allow her a moment to regain herself. Maybe to see that it isn't so bad.
He could also reverse the course and back track. Deciding that perhaps the limit being pushed isn't worth the effort at that time. Of course he will address it again later if he feels it needs to be.
Finally he can just expect that she submit to it. There's no discussion or talk. It's just understood. Doesn't mean that it's easily accepted.
Each option has their own problems depending on the situation and nothing is easily resolved. Talking and communication is the key.
But what happens when all the talk falls on deaf ears? Does the relationship implode?
Each answer just brings more questions.