Thank you ALL for your support. Here is where I am after sleeping (not very well mind you) on this.
The main thing that I think this changes for me is that I think I will now need her to admit to this at some point, not now, but sometime. I have said in the past that I didn't need that from her to move on. Now I do. I STILL believe that she will have to admit it before she can move forward with "us" so I am going to hold out for that because I think if she admits it on her own it will be better for both of us than if I confront her with what I found and introduce the whole snooping thing into it. I will NOT wait forever on this though. If we do not make progress, and if she does not admit it, I will at some point, have to let her know what I know and how I feel.
So I am not going to talk to her right now about this. I agree with those of you that said this really doesn't change anything and so why do I need to confront her? I know more now, but I already knew this so bringing it up makes no sense. I could have insisted on talking about it before this.
Also, I just want to clear one thing up. My W does not miss periods, she just fluctuates a little as to when they come. I KNOW (unless she was going WAY out of her way to fake THAT too) she had one a few weeks ago so unless she somehow suspected she could still be pregnant from sex they had before her period, that means they slept togeter pretty recently.
The really interesting thing is I took a look back at the time line of my sitch from earlier in the week. Well, what do you know, the BIG R talk...it happened the night before she bought the test. All the anxiety/panic attacks...happened the day she bought it, and the day after. Today? Well, she's sick (not THAT kind of sick) but otherwise, the anxiety and panic are gone. I can't tell her mood because she's really sick but her general stress level seems to be way lower than a few days ago.
So this all tells me that there was a VERY good reason for her stress in the beginning of the week and that the test must have been negative. I don't know what the facts are and I understand I probably won't know them any more by stressing over this OR confronting her right now.
In any event, I am STILL feeling those old sick feelings that I really thought were behind me at this point. I am still shaking a bit and feel weak. I WILL get hold of this soon because I have a wedding to shoot tonight and I can't be this way for it.
I will post some specific replies after this. Thanks you all!