Sleep phenomena like snoring may be annoying — but other nighttime occurrences are just plain bizarre (and sometimes even a little scary).

“We had a woman who tried to perform her own breast-reduction surgery” in her sleep, W. Christopher Winter, MD, medical director of Charlottesville Neurology and Sleep Medicine, tells Yahoo Health. Collectively called parasomnias, these strange sleep behaviors — which include walking, talking, and even having sex — often occur when part of the brain awakens during deep sleep but the region responsible for consciousness is still snoozing, Winter says. “Once the brain is awakened in deep sleep, all bets are off. Are you going to get up and eat? Engage in sex? Are you going to speak? Are you going to throw the baby out the window?”

Parasomnias, especially those occurring during deep sleep, tend to be hereditary, explains Shelby Harris, PsyD, director of the Sleep-Wake Disorders Center at Montefiore Medical Center in the Bronx, N.Y. However, if you suddenly develop a bizarre nighttime habit and have no prior (or family) history of it, “then you want to start looking at medical [issues] that might be causing it, as well as stress and psychiatric disorders,” she tells Yahoo Health.

Here’s a look at five strange sleep behaviors — and when they may require some medical intervention.

The classic image of a sleepwalker involves zombie-like wandering, arms outstretched, in your nightgown down a darkened hallway. But sleepwalking can actually entail much more than midnight strolls: Sleepwalkers may get behind the wheel, urinate in their closet, or even engage in violent behavior. “People have tried to jump out windows,” says Milena Pavlova, MD, an assistant professor of neurology at Harvard and medical director of the Faulkner Sleep Center.

Also called somnambulism, sleepwalking is more common in children than adults — the prevalence is as high as 17 percent in kids, but just 4 percent in adults, according to the American Academy of Sleep Medicine. There’s often a genetic component to sleepwalking, says Winter — in fact, a new study found that 62 percent of children with two sleepwalking parents developed the parasomnia, versus just 25 percent of kids without a family history of sleepwalking. However, sleep deprivation, changes in schedule, consumption of alcohol and other sedatives, hyperthyroidism, migraines, and certain meds may also be to blame. In a 2012 study in the journal Neurology, nocturnal wandering was associated with obstructive sleep apnea, use of OTC sleeping pills, depression (as well as use of SSRI antidepressants), and alcohol abuse.

When to see a doctor: Taking an occasional conked-out walk probably isn’t a problem. However, if you’re regularly roaming, you may need to adjust your surroundings to ensure your safety — install an alarm system that will sound if you head outside, put up gates, or set your mattress on the floor. If you’re still injuring yourself or leaving the house after making changes to your environment, “then you need to get evaluated,” says Harris.

“Well let’s see, I have a dodo, and a rock, and a phoenix… Oh dear! A pterodactyl, yes, the unicorn, the griffin, dear, oh yes, well, a mermaid doesn’t count, she’s out in the pool!” 

These are the ramblings of Dion McGregor, the most prolific sleep-talker researchers have ever recorded. (“It’s like being famous for wetting your bed,” he once quipped.) Although his somniloquies were often lengthy — 100 words or more — sleep-talking can vary in content, length, and intensity from person to person, says Pavlova. However, “it’s usually gibberish — not a huge narrative,” notes Harris.

Sleep talking is the most common of all parasomnias, according to a 2012 Indian study, and it’s generally considered benign. “It can be annoying for a bed partner, but it’s not hazardous,” Pavlova says. However, Winter notes one potential downside: “If you talk all night long, then there’s a good chance you’re not getting the best sleep.” Anything that fragments sleep — traveling across time zones, alcohol, late-day caffeine, stress, certain medications — can predispose you toward the behavior.

When to see a doctor: If you’re spilling your secrets in your sleep, you may want to seek help. “It’s usually cause for concern when it’s creating embarrassment for the person,” says Harris. “If people are saying things that are detrimental, then we treat it.”

A run-of-the-mill bad dream probably won’t stir you awake, but a true nightmare is terrifying enough to rouse you. “Nightmares typically happen in the last third of the night, when you have REM sleep,” says Harris. “So it’s not the deep stage of sleep. It’s in the more active brain stage of sleep, when you’re having emotional processing, memory processing, things like that.” 

Occasional nightmares are normal — up to 85 percent of adults report having had at least one in the last year. But recurring nightmares may indicate psychological trauma: For example, if you were the victim of a mugging, you may find yourself reliving it in your sleep. Alternatively, they can be a sign of a breathing problem, like sleep apnea. When you start to dream, and your body becomes paralyzed, the muscles that hold open your airway may stop doing their job, explains Winter. “So the airway collapses during the dream, and your brain takes that feeling of suffocation and incorporates it into the theme of the dream.”

When to see a doctor: Frequent nighttime freak-outs that leave you feeling distressed may warrant a visit to the doctor: “It’s sort of like a migraine — once in a while isn’t a problem,” says Winter. “But if you’re having more than two or three a week, that would be cause for concern.”

Researchers say sexsomnia may occur when you’re having a sex dream — or because you’ve been feeling a little sexually frustrated lately, says Winter. “If a person is hungry, they’re going to eat,” he says. “If it’s been a while since they’d had sex, they may want to do that. I think sexsomnia is often feeding on underlying issues.” In the Canadian study, sexsomnia was associated with the use of illicit drugs and alcohol.

When to see a doctor: If your partner is fine with sleepy sex, then sexsomnia may be more funny than freaky. However, “a lot of times, the partner is out of it, too, so it’s not necessarily consensual,” says Winter. That’s when sexsomnia becomes problematic and should be addressed by a doctor.

If you’re leaving your bed to chow down while fast asleep, it’s not as if you’re simply preparing breakfast a few hours early: One of the hallmarks of sleep-related eating disorder, as it’s officially known, is eating strange things. “A lot of times people consume odd combinations of food or even inedible or toxic substances,” says Harris. “I’ve had patients eating coffee grounds or Ajax in the middle of the night.” Although you won’t remember scarfing a cigarette sandwich, the state of your kitchen will likely reveal your midnight binge-fest: “People are very messy when they’re sleep-eating,” Harris says.

In some cases, sleep-eating is simply a variation of sleepwalking. “A lot of sleepwalking behaviors tend to be things that you do routinely,” eating included, says Harris. However, it can also commonly be caused by sleep meds, like Ambien and Lunesta.

When to see a doctor: If you find that you have no appetite in the a.m., yet you’re gaining weight, sleep-eating may be to blame. Since your health is at stake if you pack on the pounds, you should seek help (not to mention that you may be eating inedible, or even dangerous, substances without realizing it).