Sleep paralysis, a feeling of being conscious and unable to move, hits sleep-deprived hard

One moment, you're peacefully sleeping. The next, you're awake and paralyzed - unable to move, breathe or scream as you begin to see shadows in the dark.

Your brain goes into overdrive, producing hallucinations of intruders, alien abductions and sometimes out-of-body experiences.

No, you're not going crazy. You're simply having a sleep paralytic event.

'It's a normal brain stem phenomenon,” assures Dr. Mark Eric Dyken, neurologist at University of Iowa's Sleep Disorders Clinic.

The disorder usually is associated with narcolepsy, but Dyken says it's not unheard of for someone to experience it at least once in their life, especially if they're sleep deprived.

A 2011 review of studies published in Sleep Medicine Review revealed that 7.6 percent of the general population experiences sleep paralysis at least once in their lifetime. It's even more common in students - a population not surprisingly sleep deprived - at 28.3 percent. The percentage is even higher in people with psychiatric disorders, at 31.9 percent, and particularly high in those with panic disorder: 34.6 percent.

Recurrent sleep paralysis not associated with other sleep disorders, or 'isolated sleep paralysis,” is more rare.

When we deprive our bodies of sleep, especially the most restorative sleep cycle, rapid eye movement (REM), it starts to do funky things.

It usually takes 60 to 90 minutes to enter REM sleep, but if you're really sleep deprived, your body will 'nose dive” into it, Dyken says. The paralysis that follows is a natural process of REM that keeps you from acting out your dreams.

Sleep paralysis also can occur when waking up, if a REM cycle suddenly is disrupted.

Whether you've fallen directly into REM or waked from it, your body still thinks you're asleep, which is why you remain paralyzed. Meanwhile, your brain is awake and active. Realizing your paralysis, you begin to panic - for all you know, it's permanent.

As you lay there in a half-sleep state, paralyzed and panicking, your brain begins to produce visual, auditory and sometimes physical hallucinations that almost always are scary.

The most common hallucination is the 'intruder,” usually described as a shadowy figure lurking in the dark. Another, 'the incubus,” is a little demon that sits on your chest and suffocates you - as famously depicted in the 1781 painting 'The Nightmare” by Henry Fuseli, just one of many historical references to the disorder.

More rarely, people might experience sensations of floating, or looking down upon their body. Some believe they're being abducted by aliens, possessed by spirits or being held down.

Though the paralysis can feel like forever, it usually lasts mere minutes.

Dyken thinks the disorder is not commonly known, mostly because of the stigma associated with its unusual symptoms.

'People are going to think you're nuts,” he says. 'No one wants to be afraid to go to sleep, so they hide it.”

Matt Rissi, a local DJ and Hibu salesman, says his wife teases him about his sleep paralysis episodes. He's had it at least 10 times, which isn't surprising considering his unreliable sleep schedule ­- sometimes going without sleep for a day or more and 'power sleeping” for 12 hours when he gets the chance. But, he says, it hasn't happened in a couple years.

'The experience itself is so surreal ... but very real,” he says. In one episode he saw a 'wicked figure” standing next to him, moving left to right and making a 'heavy fluttering noise,” almost like a hummingbird but louder.

'I was paralyzed and was trying to jerk myself out of it,” he says. 'I remember really focusing on trying to flip over ... like trying to will myself awake.”

His wife heard his muffled attempts to scream. Concerned, she shook him awake.

'When you start to come through, you realize you're in your room and not crazy ... It sounds so funny,” he says. 'Obviously there wasn't a mothman floating around my bedroom ... but when you're in that sleep stage, you're kind of questioning reality.”

Similar accounts litter Internet forums, as well as historical references like that of Dutch physician Isbrand van Diemerbroek, who in 1664 described a patient's symptoms as 'the devil lay upon her and held her down,” diagnosing her with 'Night-Mare.”

If episodes become frequent, it's time to see a specialist - though sleep paralysis itself is not dangerous to your health.

'If it happens once in a blue moon and you feel like you sleep well, you're not tired, don't have trouble concentrating or have dysfunctional behavior, fine,” says Dr. Andrew Peterson, medical director at the Eastern Iowa Sleep Center. But if you start feeling moody, irritable, depressed, like you're not able to get along socially or you can't concentrate, then there could be a deeper issue, he says.

'People tend to downplay their sleepiness,” Peterson says. 'Saying you're sleepy is like saying you're a wimp, socially.”

So instead of getting the sleep they need, they reach for another cup of coffee. But if you don't make it a priority, or if you frequently disrupt your circadian rhythm with late nights and early alarms, your body is not going to perform as optimally, doctors say.

'You need air, food and sleep to keep alive. If you try to cheat mother nature, you will fall asleep driving a car, or at work - bad things happen when people fall asleep at the wrong time,” Dyken says.

The best thing you can do to treat sleep paralysis is to get better sleep.

Peterson suggests keeping a sleep diary, making sure you're going to bed and waking up at the same time every day and spending enough time in bed - eight hours if you're 25 or older, nine if you're younger.

There are some antidepressants that have a REM delaying or suppressing effect. But, Dyken warns, no drug is without side effects.

'Good sleep hygiene is the best medicine,” he concludes.