5 weird things that can happen in your sleep

Oct. 10, 2012 at 9:06 AM ET

Most of us have our fair share of wacky dreams involving everything from time machines to tutu-wearing trees. But check out some of the other strange phenomenon that can take place while we're sawing logs.

Sleep paralysis: During REM sleep, our bodies are essentially paralyzed (otherwise, we'd be physically acting out our dreams). But five percent of the population will occasionally get caught either going in or coming out of REM sleep. As a result, their body is paralyzed while their mind is mostly awake. This can be especially upsetting because sleep paralysis is often accompanied by waking dreams.

Waking dreams:  Officially known as hypnagogic (pre-sleep) or hypnopompic (post-sleep) hallucinations, waking dreams can involve anything from the sound of someone knocking to the sight of a monster creeping ever closer to the bed. Lasting anywhere from a few seconds to a few minutes, these weird waking dreams can be triggered by lack of sleep (especially if you have a genetic predisposition for the condition). Some researchers believe these hallucinations are responsible for our persistent tales of witches, ghosts and alien abductions.

Exploding head syndrome: Despite the name, this condition does not involve your head flying apart but rather audio hallucinations that occur while you sleep. "It's fairly rare," says Russell Rosenberg, chairman of the National Sleep Foundation and a board certified sleep specialist. "The person wakes up feeling like they've heard an explosion go off, like a bomb. But there's nothing in their environment that's caused the noise. It's totally internal." Rosenberg says no one knows what the direct cause is but exploding head syndrome is most likely exacerbated by stress.      

Sleep walking/sleep eating/sleep sex: These behaviors all fall under the umbrella category of non-REM parasomnias, says Rosenberg. Patients will walk outside without any clothes on, cook food, take a shower, get ready for work, or even have sex (with a partner or stranger) -- all while sound asleep. Rosenberg says they can be brought on by stress or medications or some other unknown cause. "But not everybody is going to have them," he says. "There's a genetic component but we don't know exactly what it is."

REM behavior disorder: People who don't experience paralysis during dream sleep can be at risk for REM behavior disorder, which can cause them to act out their dreams, for instance, choking a spouse while having a dream someone's attacking them. David K. Randall, author of Dreamland: Adventures in the Strange Science of Sleep, says in some cases people have actually committed murder in their sleep. "In the late 1980s, there was a famous case in Canada where a man drove 14 miles to his in-laws house," he says. "He stabbed his mother-in-law to death and almost killed his father-in-law, but his lawyers convinced the jury he was sleep walking and he was acquitted." Rosenberg says REM behavior disorder could be triggered by a stroke, a tumor, or a genetic abnormality. In a nutshell, "The brain is not doing its job," he says.

More from NBC's Healthy Week series:

What to eat to get a good night's sleep

The worst sleep offenders and how to rid them