Why Some People Kill in Their Sleep

During REM sleep, the body is paralyzed so that the sleeper does not act out his dreams, but when this phenomenon malfunctions, bizarre sleep disorders like sleep paralysis and REM Behavior Disorder may arise.

Question: What is sleep paralysis?
Shelby Harris: Sleep paralysis is something that is actually very common.  Many people have it, I've had it myself.  And what happens is, when you're in that REM stage of sleep, your brain is very active.  You're dreaming your most during that stage, you're mind, your eyes are moving, there's a lot going on.  It's like fireworks going on in your brain.  Now, what happens in the rest of your body, and this is an evolutionary function, is that your body has muscle atonia, meaning your muscles are basically turned off.  You can't work.  So, you're brain is active, your muscles can't work.  
Now for what happens in sleep paralysis is that some patients, and we'll notice this earlier in the morning because you're having more REM sleep then, will wake up in the middle of REM sleep.  So, I know myself, I woke up once in the middle of REM sleep and I couldn't move my muscles.  And it was very scary.  And it's scary for anyone who has it because you're mind is very active, your eyes are active, but nothing else is moving.  So you have to give yourself a little while.  You'll come out of the REM sleep and you're muscle will awaken and it's find.  It's a totally normal thing to have.  
Now, it can be indicative sometimes of other sleep disorders, so we'll see that a lot in narcolepsies.  Some patients will report that they have sleep paralysis.  If we see sleep paralysis alone and nothing else, we don't really think all that much of it, but if we see other symptoms, then it might be a red flag for something else that's going on.
Question: What happens if our muscles aren't paralyzed during REM sleep?
Shelby Harris: So REM Behavior Disorder, RBD.  It's newer diagnosis, I'd say probably about the past 10 or 15 years, we're really recognizing it more and more.  Patients will come to our practice and they'll say, "I'm waking up in the morning and, I have bruising on my arms.  My fists are bloody" or they'll say, "My house was a mess.  I found things all over the place."  Generally that could be sleep walking, but sleep walking tends to not be as violent.  And that's earlier in the night when you are in the deep stages of sleep.  In RBD, it tends to be a bit more violent, a bit more aggressive.  So when you are in REM sleep, you're muscles are supposed to have atonia, and no function for them, but for some patients their muscles don't turn off.  So if they're having nightmare or a very vivid dream, they'll actually act out -- essentially their dream in their sleep during REM sleep.  So that's why we'll start to see patients come in with bruises, their bed's a mess, they might fall out of bed, things like that.  So it can be, for some patients, a very violent problem that we actually need to treat them aggressively. 
Question: Have there been court cases in which RBD has been blamed? 
Shelby Harris: Yeah.  There are some that are -- REM Behavior Disorder, we'll see some court documented cases.  And they really need to have a thorough evaluation with a sleep specialist.  You can't just say, "Oh, it was while I was sleeping."  There's confusional arousals, there are states in deeper sleep that can happen where people will go and they'll disappear and they'll take on some other persona.  They'll commit some crime, but it's all when they are in a very deep stage of sleep.  So you really need to have a very thorough evaluation.  But yes, there is a line of work of people who work with people who have been charged with crimes and we'll actually do a sleep disorder analyses with them.