I concur with Christina and Hankster and want to point out what exactly the abuser did (it seems). It is more than physical abuse.

So she slapped you and you, instead of feeling insulted, wonder as to the depths of her psyche. Because it was out of nowhere, you are puzzled, you doubt your own judgment, and you need the wisdom of anonymous crowds on the internet to answer a very simple, straightforward question. I have seen you around and your judgment has always been good, and then this query is REALLY out of nowhere.

So I would examine what else has been going on and how you have arrived at this station in your life when you all of a sudden lose all your otherwise good judgment and start asking such questions. To me (and I was a victim of non-physical abuse) it sounds as if your partner, somehow and I do not know how, managed to completely erode your confidence and your ability to think for yourself and call a spade a spade. Seems like some deep-seated emotional abuse. As if she managed to make you blind.