Ooooh, thought of a new one to add to the list:
Writing causes insomnia. You stay up into the wee hours of the morning writing, then head off to bed but can't sleep (despite being exhausted) because your mind is whirring with more ideas/replaying what you have written.
Also:
You act out scenes or dialogue or motions in order to make sure that the descriptions are accurate or that they work overall.
