I'll admit, I was operating on about four continuous hours of sleep a night in the six months post-birth, a far cry from the seven I require to feel rested and better equipped to handle life's demands, parental or otherwise. It wasn't until my daughter started sleeping through the night that my circuitry got the reboot it needed and the daymares wound down.

Kennedy-Moore, author of "What About Me?: 12 Ways to Get Your Parents' Attention Without Hitting Your Sister," also advises moms to go easy on themselves when dark thoughts invade.

"It's important to remember that thoughts are not the same as actions," she said. "Just because you can imagine your baby falling does not make it likely that your baby will fall. Although in some cases, dark thoughts can be a severe and debilitating symptom of a postpartum anxiety or depressive disorder, usually they are just an unpleasant part of normal adjustment."

She also said it's helpful to remind yourself that you're not a bad mother, you likely just have a vivid imagination.

"Don't try to fight the thoughts. The more we try not to think something, the more it will pop into our heads. Just notice the thought and gently let it pass."

And for the love of your own sanity, don't be afraid to talk to someone about it (and in severe cases, this is a must). A therapist. A nurse. I really wish I had opened up about it at the time.

As it turned out, I did find a measure of relief from a fellow mom, albeit one I didn't know. Actress Tilda Swinton, who has twins, had sobering words about motherhood when talking about her role in the chilling film "We Need to Talk About Kevin."

Swinton said parents often shy away from discussing taboo subjects, such as the fear that their children will turn out to be violent or that bad things will happen to their family. She described how her fierce maternal instinct kicked in after giving birth, which was both terrifying and exhilarating.

When I met Swinton at an art gallery opening not long after the film was released (I interviewed her boyfriend, the painter Sandro Kopp), I wanted to hug her (though I didn't dare -- her white suit was too awesome to crush). She helped me see I wasn't necessarily losing my mind, just creating a slightly new one.

Brizendine said she believes there's a silver lining to those horrifying, violent thoughts.

"This level of intense feeling of aggression shows you how intensely bonded you are to your baby," she said. "That's the good news. This is a proof positive of that emotional and biological bond."