Your stress level can have a significant (negative) impact on your creative output. But of course, it’s not possible to avoid it, at least not entirely and all the time.
When it strikes, your best bet might be to acknowledge it, accept it and try to define the steps you could take to ease it up. It will give you a sense of control, which will free up your mental power for more important things.
And if there isn’t anything that you can do about it, you’ll still have the comfort of knowing that you did your best to deal with it. Again, this will help you regain a sense of control, which will free up your mental power for more important things.
Either way, don’t stress about it.