This is something that my editor has been helping me see and understand over the last few months, and finally I see it.
YOU DO YOUR BEST WORK WHEN CALM. PERIOD.
I thought when you got anxious, you screwed up. As in, fear gets in the way, you get blocked, and so on. Nope. When you get excited, you screw up too. Any emotional imbalance that throws you out of whack is bad for writing.
Yes, I know, everyone loves talking about how you have to feel what you write. But the truth is, you don't have to feel it, you have to act out your characters while following the structure (so it's different from simply acting out whatever you feel like), and for that you have to be very very calm, as in, calm before the storm. And you have to switch from character to character. Ask any of your professionally acting friends how they do it, see what they tell you.
So excitement about your story is as bad as anxiety. Only calm produces good results.
What gets you calm?
(For me it's walking or biking or simply getting away from the screens and staring at the sky or grass or bugs.)