Hi scardycat, I'm sorry you had such a bad day, but you did the best you could considering the circumstances/the way you were feeling, right? So you really can't fault yourself on that!!
Now that was today, just try not to let it impact on the next day you're working, that's a whole 'nother day, right? Just because it was bad today, doesn't necessarily mean it has to be bad another day.
In general have you got any techniques that can help you a little with the anxiety though, or could you look for a few more?? Maybe with the help of a T as well??
If you have to change jobs though, that doesn't mean that you're hopeless or useless at all, that just means that this might not be the right job for you. So time, just like for some other people who aren't happy in their jobs and want a change, to start looking for something else.
Alison