Clash of Chemistry and Reality

The other day someone asked me how I know I'm attracted to another person. I realized the answer might be of interest, so here you go.
First, whether sighted or not, physical attraction comes in many forms. While you might think it's dependent upon vision, in actuality that's not the case. If physical chemistry were reliant upon sight, everyone would have sex with the lights on. Internet dating in the mid 1990s illustrates my point. Back then, pictures were not posted online. You did it via the U.S. Postal Service. Long before people's images had wended their way back and forth, attractions began to grow. I'm not saying people didn't want that visual confirmation of chemistry, but they did feel a zing despite no visual input.
For me, attraction is a very indefinable thing composed of how a person treats me, their manner in general, and how I feel in their presence. I have been known to react to chemistry after thirty seconds. Or less. People give off some unnamable thing that I perceive and interpret without conscious thought.
It's not pheromones, which require a functional olfactory system that I do not possess. It's not dependent upon touch for it often happens prior to physical contact. It's not even a case of being so desperate that I'll go for anyone who treats me well. Something happens on dare I say animal level and my hormones start parting.
Now, here's the interesting part. That chemistry can fade in the face of actual physical exploration. People feel..... odd. It might be because I don't go around feeling people regularly. Perhaps I get an image in my mind and the reality doesn't match. Possibly I have emotional chemistry with someone but not physical. Whatever the case, it's rather disconcerting.
Imagine, for a moment, what happens. I am attracted to some person and it seems to be mutual. Eventually, things go from hand-holding to more. The first time I touch someone's face can be kind of a turn off. So, there I am, having my first physically intimate experience with someone and while they are touching what they have already known through sight, I'm getting my first "look." Should it not be what I thought, then I'm suddenly torn between how it felt five seconds ago before initial contact and how I feel at the present. Totally ruins the moment for me.
There has only been one time in my life where I didn't have chemistry with someone at first meeting rather growing over time. To be precise, about three years. Suddenly, my hormones woke up and started paying attention. Surprised me.
The great part of that experience was discovering feelings evolving in such a way somehow become independent from the physical. It's THIS person under my fingertips and that feeling can overpower the actual sensory input.
I've unfortunately come to the conclusion that if I don't want that moment of dissidence between the intangible chemistry and reaction to the physical reality, then I have to wait until I know I will be touching someone for whom I have strong feelings.