You get a writer's 'high' when:
You find just the right word to bring a sentence together.
You read through what you wrote the previous day and decide; 'it's really quite good.'
People line up for you to sign your book after giving a talk (three people do constitute a line - don't they?
You read an excerpt from your children's book to a class and they listen attentively and laugh in the right places.
You get fan mail from children