I reacted that way (getting hysterical, breaking down crying without any forewarning) the first time my Dom spit in my face. No one ever had dared do that, or even dared to suggest it.
Yet, I have been provoking him into it ever and ever again since then (I cannot get my guts up to ASK for it because I have issues with asking for things during a scene *g*).

And yes, it can be VERY erotic to feel unsettled! I agree with Ozme here.
In case you wondered: No, you are not weird :-)

Then again, this is my first BDSM relationship. We are together for 10 years now, and I donīt remember ever having used my safeword; I do remember MANY times considering using it, though.
Some other Dom in here wrote once that this is a sign of your Dom leading you to your limits, and therefore a good thing.
A good Dom (like mine) will develop a feeling for when he should stop without you using the safeword. There are times when the sub does not know when to stop or slow down or something is actually getting too hard on her because she is too lost in her own excitement.

It is also possible for a Dom having to use a safeword, as Doms also have limits. They are not Gods, you know :-)

As for the safeword: It is absolutely vital in my opinion. It does not mean you will use it if itīs not really serious. It is a possibility to stop a scene if it really gets too intense or hurtful to be enjoyable anymore. There are taboos in each of us we might not even be aware of until they get tested.
In your own interest, and in your Domīs interest, I would advise you to agree on a safeword.
If you trust him, and he trusts you, you can both be sure it will not be spoken unnecessarily. But it is useful as it takes away some fear/insecurity on your side, and it will prove security for him. Doms are not mind-readers. It is a matter of fairness to your Dom to provide him with a definite way of knowing when he is going too far.

Another way that may work for you is something I read about here a few times. I find the idea appealing. Itīs sort of a traffic-light-word-system: green is for "all is fine", yellow is for "this is too painful/too scary right now, please go slower", and red is for "stop right now - end the scene - we need to talk".
Of course you can use other expressions instead of the colours, but you get what I mean, I hope.

Kind regards
Arria