Your Grace, I hate that you have to struggle with this. I have a close friend who is dealing with similar and she's gone into detail about her issues. I can't imagine how I'd deal with it if it were me.
LadyV, once you start worrying about being fired, you make your day that much worse. I've been under the gun before with jobs. One job, I should have just quit as soon as it became clear the manager and her friends wanted me gone, because it was far too much stress for what I was getting paid. Lesson learned.
But I can tell you this much--the last few times it happened, I just did my job and didn't care. There's an old saying: If you're on thin ice, you might as well dance. Meaning don't be afraid of what might happen and just do your thing. Besides, I'm sure you'll be fine. You're a good employee for them.