Here's a little writer's hint that has saved me tons of time and anxiety:
You're chugging along like the Little Engine Who Could, writing copy, and suddenly find you can't think of the right word. Don't struggle with it more than a few seconds. Just use the word "lobster" -- and move on. You'll fix it later.
You can waste a lot of time and energy on a futile search for a certain word that you just know exists, but you can't think of it. I promise you those elusive words are easier when you come back later.