The celebrated Swedish physician Axel Munthe, who had more success treating the insomnia of his patients than he did his own, wrote in his 1929 bestseller, "The Story of San Michele":

"Insomnia does not kill its man unless he kills himself -- sleeplessness is the most common cause of suicide. But it kills his joie de vivre, it saps his strength, it sucks the blood from his brain and from his heart like a vampire."

We've been taught to see insomnia as secondary to, as resulting from, depression, neurosis or other sorts of psychopathology. But there is increasing evidence that it may work the other way around:

Insomnia may be the cause and not the consequence of a person's emotional instability. Insomnia is now known to be a risk factor for depression, alcoholism and suicide.