You said you auditioned for a show last year but they didn't think you could handle the stress, but now a year later, they called you back up asking you to be in it after all?  What's the problem with that?  Isn't that what you wanted, or are you freaking out because of the lack of time you're going to have?  Do you know for sure that you're going to get a very substantial part?

Honestly, the thing you should do is go down there and see what's going on.  Get the details and evaluate whether you think you can do them or not.  If you think you can, even with some hard work, then go for it.  If not, then tell them straight up when you're there that you can't do it and to look elsewhere.  It won't be your fault if you can't - remember, they're the ones who called you up on such short notice.