Dear Dream Doctor,

I started my night’s sleep thinking of spiders. I knew there were no spiders in my bed, or for that matter on my feet. Regardless, I kept thinking there was as I was drifting on and off to sleep. I pulled the covers off of me 3 times to check. The spider I was dreaming or thinking about is what we call a “Daddy Long Legs.”

(We had company over a month ago and a person said that a daddy long legs was a poisonous spider).

I finally got through that part and in early morning, around 6:30am, I found myself dreaming that I was going to step on a snake in some type of garden. I jumped in my dream. The next thing I knew I was throwing my covers off of me as I tried to get away.

I did get away from the snake but I hit my head, leg and arm on my end table with such force that now I have a giant bump on my head—and a cut. I don’t recall how I did this. What I do know it was a life and death situation. I guess that is what bothers me the most.

I can’t figure how I hurt myself in all those places when I was still asleep. (I think?) I yelled out in pain, and then realized I was alone since my husband had gone to play golf. I was so sleepy that I went back to sleep. I awoke later to a giant bump and pain.

I do live in the country and my neighbor just killed a snake a week ago, but I was so shocked by the intensity of the dream and what I did to myself in the process. Was this just dumb luck?

—Mary Ann, Age 49, Canton, GA, USA

Hi Mary Ann—

No, I don’t think your hitting your head was “dumb luck.” Rather, it actually is a classic instance of REM Behavior Disorder—a disorder which we have seen appear in this column more than once. In your case, though, you hurt yourself in the process of “acting out your dream,” and this is what we always fear with this disorder.

REM Behavior Disorder is a failure of the body to completely intercept the commands for movement that are routinely generated by our brains during Dreaming, or REM sleep. In a famous experiment performed on cats by the French researcher Michael Jouvet in 1963, Jouvet lesioned the location in the brainstem that is responsible for intercepting these signals. When the cats recovered from surgery, remarkably enough, they all demonstrated REM Behavior Disorder. Which is to say that, instead of sleeping peacefully through their dreams, the cats actually got up and began acting them out. Most of the activity observed was what one normally sees in developing kittens—play fighting, pouncing and leaping—but this time the play was all performed with imaginary objects.

REM sleep is remarkably uniform across all warm-blooded creatures. Cats, dogs, wolves, horses, bears—we all dream. And we all experience the concurrent loss of muscle tone that, coupled with the activation of the dreaming brain, is so defining of REM sleep. But the dampening of motor response to the commands for movement is imperfect. Cats twitch their whiskers; dogs “run” in their sleep. Surely horses and bears experience the same twitches and jerks. In humans, REM Behavior Disorder commonly manifests itself as sleep-talking. The mouth and vocal cords are not “turned off,” and so we vocalize our dreams. In more severe cases, people actually get out of bed and run around the room. When this happens, the disorder—as you well know—can become dangerous.