every one has bad days, but her bad day cost YOU money.  chances are it will happen again, when that will be who knows, but IT WILL happen again. you gotta ask yourself if you wanna keep seeing her and hope for the best or just move on.  
I myself had this happen, and while i did see her after that happened, it wasn't long before things got progressively worse with her.  you really never know what is going on in a providers head let alone a womans head.  it can be hard to walk away after you have had countless wonderful times, and one bump in the road, trust me, i been there. but in my experience, that nice paved road with a little bump...well it ran out and i was going down a bumpy dirt road before i knew what happened and i regretted not stopping seeing her sooner to preserve a happy memory of her, cause i had great times with her.

i could be wrong though.

How did she resond to your email.

If she's had time to answer you she should be able to be open to giving you an explanation.  If she has not respond I've move on.

Doc

and as long as it didn't involve knives or guns, I'd let it go as long as you are basically satisfied with the gal in question.

Then there is the slow tappering off in perfomance situation.  We clients are consumers, and it is our responsibilty to set standards for the product we purchase.

I see one gal whom I've known many years, and whom I enjoy immensely, but over time I started to notice a bit of slackening in her performance.  Let's face it, sex work can be a bit of a challenge, physically and mentally, when done right.  If the gal thinks that she can spend most of a two hour session just chatting or laying there without you minding, there's a good chance that she will do so.

I am by nature adverse to confrontation, so I decided to let it slide at first.  Then I noticed that I was becoming annoyed with the situation and decided that maybe I should just find a new favorite to replace her, but I decided that I would rather get our sessions back to the state they were in when we first met.  So, I spoke to her about it, and lo and behold she understood and accepted my criticisms and now I'm one happy client again.  This is a win/win situation.

On the other hand, I had another favorite where the same situation developed and the discussion did not go smoothly.  It descended into defensiveness and recriminations.  The solution there was obvious, I pulled the plug on that.

Lesson to be learned:  Communicate clearly and unemotionally on what it is you want and expect.  If the gal is worth her salt, she will come through.

Otherwise, it's a big ocean out there guys.

I hope this helps.

staying cool right now is great advice. you don't want to lay a lot of emotional drama on her that might scare her away. you want to keep her as an option right? don't burn your bridges. fall back, regroup, give it some time, advance with care. keep on the high road.

Or redefine what an ATF is. My ATF is such because we communicate very well both in bed and out. If our encounter is ever less than spectacular she will usually apologize to me without me saying a word! And I do the same if I have an 'off' day.

It's all about respect. We each want the other to have an enjoyable experience whenever we meet. If there is no respect, it is time to move on or lower your expectations.

I think you just got the real GFE

Or the wife experience.  Take a break and let the anticipation build up again.