CHICAGO (CBS) -- You wake up and try to get out of bed, but find that you can't move -- you're paralyzed.
It's a frightening condition that CBS 2's Marissa Bailey found is more common than you might think, in tonight's HealthWatch.
For some people, hours supposed to be spent sleeping peacefully are instead hours of horror.
They wake up to a literal nightmare, unable to do anything about it.
"It's just a really scary experience," Lilly Altamirano says.
The disorder is called "Sleep Paralysis." People who suffer from it are awake, but unable to move.
Altamirano has experienced it since she was a child. "Sometimes it's a prison, my whole body's a prison," she says.
Tim Hall had only one episode, but the experience is still vivid.
"All of a sudden, I wake up and I couldn't move at all," he remembers.
And what makes it even worse is horrifying hallucinations.
Scary, menacing shadow people that seem real. And the people experiencing this are helpless to do anything about it.
"When I see them come toward me, I'm just like...I'm terrified," Altamirano says. "It's like being tied up in a straight jacket and then you feel like there's a stranger in your room," Hall recalls.
Researchers say sleep paralysis occurs when the body is moving out of rapid eye movement or REM sleep. The person is awake, but for some unknown reason, the body's ability to move is not yet activated.
Estimates are that anywhere from 5-25 percent of people experience sleep paralysis in their lifetime.
"It's so vivid it's so realistic and it's so scary," a patient said.
Northwestern University sleep expert Dr. Phyllis Zee says the disorder is not harmful, and she says there are ways to get through it with less fear.
"Having sleep paralysis does not mean there's anything bad going on with you. It doesn't herald any major sleep disorder," Zee says. "If you're prone to sleep paralysis avoid medications especially if you have narcolepsy...you want to avoid caffeine things that can disrupt your sleep... anything that make your sleep more fragmented can increase your experience in sleep paralysis."
Sleep paralysis often occurs during periods of sleep deprivation and stress. Establishing a regular sleep schedule helps as does sleeping on your side instead of your back.
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