Keith Richards, master guitarist for the Rolling Stones, sleepswith his guitars.
Andy Johns, the band's engineer, reported that Richards, a perfectionist if ever there was one, was so into the music that he would often sit in a chair for twelve hours straight, playing a song over and over. Then he'd collapse into bed, guitar by his side. In the middle of the night he'd sometimes wake up and call Andy and tell him to get back into the studio. He had a brainstorm in his sleep. That's how the classic "Tumbling Dice" was recorded—in the wee hours of the morning.
The relevance for a writer should be clear. You're more apt to make progress with a work if it obsesses you. Like Keith Richards, you're going to have a breakthrough and inspiration will be more frequent if you let this good kind of obsession into your life. You can learn from the example of Keith Richards. Maybe keeping a notebook near your bed so that you can record inspirational thoughts might be one trick that helps you capture great ideas. (Keith keeps a tape recorder by his bed.) SF writer A.E. van Vogt used to set an alarm clock to wake himself up during the night. Then he'd record his dreams and nightmares in his notebook and use them to plot novels. Edgar Rice Burroughs, inventor of Tarzan, also used dreams to plot. These writers were obsessed with their stories. Can you say the same?
Writers at work
There are any number of writers who were obsessed with their stories. D.H. Lawrence was obsessed with the characters in Women in Love. He wrote five drafts of the novel, often starting from page one and rewriting everything! J.D. Salinger used to tell his daughter that he knew what Holden was doing. Faulkner quoted his characters to friends. These writers were immersed in their fictional worlds so completely that they sometimes confused fiction with reality.
The same kind of preoccupation can pay huge dividends for writers of nonfiction. The idea is to let the work get under your skin. In this way, you'll be in league with the greats. From Keith Richards to Balzac to Faulkner, you'll be doing what all great creative artists do: focusing on your work to the point where it becomes almost an obsession.