I too agree with Kitt. It's hard to let the kids down - I myself have had the same kind of dilemmas this week. Try to use some of the suggestions Kitt gave you - 6 year-olds are easier to persuade to do other things, their attention can easily (usually) be redirected to something else. Just pick a couple of things that you know you would be able to handle ok and give her those to choose from. Then you can both get to have some fun that won't be so stressful for you.
Please don't beat yourself up or feel guilty (I should practice what I preach ). This is not something you asked for and you just have to deal with it and work on it the best you can. I know it's hard for young kids to understand these things, but if you can describe to her how you feel about places like Luna Park using words that she can understand at her age, it might help her to understand it a little better. She'll forget it and you'll have to explain again, but that's ok - you're just reinforcing it her. But don't forget to tell her that you are working on getting better and you'll be to do more things as time goes on.
I actually had a similar talk with my teenagers last night, because my son is very worried about me and I'm trying to ease that worry for him. But they both are trying to understand how things are for me and they seem to be doing a pretty good job at too. Sometimes they get disappointed if I can't attend a function of theirs, but they say they understand why. I know my kids are quite a bit older than yours, but the explanations are somewhat similar.
I hope this helps a little - let us know how it goes.
I have: Agoraphobia, Barrett's Esophagus, Bipolar Disorder, Depression, Fibromyalgia, Panic/Anxiety Disorders, Restless Leg Syndrome, Severe Acid Reflux, Sleep Apnea, and Social Anxiety
Meds: Ambien CR, Ativan, Flexeril, Lamictal, Lexapro, Neurontin, Nexium, Requip, Ritalin ER
A slip of the foot you may soon recover,
but a slip of the tongue you may never get over.