E News Kendall Jenner opened up about struggling with sleep paralysis -- a phenomenon where your body is paralyzed, but you are awake and people tend to hallucinate and experience nightmares.

On Sunday, Kendall Jenner opened up about struggling with a sleep problem that is thought to affect nearly eight percent of the general population: sleep paralysis.

“I wake up in the middle of the night and I can’t move,” Jenner said in the latest episode of Keeping Up With the Kardashians. “I’m freaking out.”

Indeed, sleep paralysis is a phenomenon where you are awake and conscious, but your body is paralyzed (except for your eyes) and between 80 and 90 percent of the time you experience nightmares or disturbing hallucinations.

“They [can be] scary experiences,” Brian A. Sharpless, associate professor at the American School of Professional Psychology at Argosy University and author of Sleep Paralysis, told The Huffington Post.

Episodes happen during your lightest stage of sleep ― rapid eye movement sleep (REM), during which you dream ― and can last anywhere from a few seconds to a few (terrifying!) minutes.

Experts aren’t sure what causes sleep paralysis, but they suspect stress and anything that disrupts your sleep in the first place ― including alcohol, caffeine or jet lag ― can increase your risk of experiencing the phenomenon. Sleep paralysis can also be a symptom of other, more serious sleep disorders and mental health conditions, like insomnia, narcolepsy, anxiety disorders, panic disorder and post-traumatic stress disorder (PTSD).

“Everyone says I’m fine, but I don’t feel fine.” - Kendall Jenner

Sharpless is not Jenner’s doctor, but he noted that several struggles Jenner discussed in the show, such as anxiety and jet lag, can increase the risk of experiencing the scary episodes.

“Everyone says I’m fine, but I don’t feel fine,” Jenner told her mother Kris Jenner on the show.

The episodes can be terrifying, Sharpless said. But for most people, sleep paralysis episodes are a one-time or occasional experience ― and they’re not necessarily a problem or dangerous.

Here are four other important facts about sleep paralysis:

1. Sleep paralysis is more common in people with mental health problems

Research has suggested sleep paralysis is way more common in people with mental health issues and young adults, affecting more than 28 percent of students, nearly 32 percent of psychiatric patients and nearly 35 percent of people with panic disorder.

2. For most people, it’s NOT a chronic condition problem

Estimates suggest that somewhere between 15 and 45 percent of people with sleep paralysis experience such episodes repeatedly, and not as a side effect of another sleep disorder or condition ― which is known as recurrent isolated sleep paralysis. People with the recurrent condition also tend to have trouble with sleep because of the episodes, such as trouble falling asleep or avoiding sleep out of fear.

“You don’t have the disorder if it just happens once,” Sharpless said. “And it has to actually be affecting your behavior [to be recurrent isolated sleep paralysis].”

3. Good sleep behaviors help prevent sleep paralysis

Practicing good sleep behavior like skipping alcohol and caffeine before heading to bed and waking up and going to bed at the same time everyday can help anyone avoid sleep paralysis.

Another tip: sleep on your side, Sharpless said. Sleeping on your back or stomach make sleep paralysis way more likely, he explained.

4. If it is a problem, a specialist may be able to help

And for people with the recurrent condition, a sleep medicine specialist or psychologist may be able to prescribe medications that help suppress REM sleep (and therefore help people avoid sleep paralysis).

Taking the simple steps of getting on a regular sleep schedule, skipping alcohol and caffeine before bed and sleeping on her side, all might help Jenner’s episodes go away, Sharpless said.

And if those fixes don’t help, he said Jenner (or anyone experiencing similar symptoms) should consider seeing a sleep medicine specialist or psychologist who could help determine if the episodes are something more serious.

Watch Jenner open up about her symptoms in this E! News video about the episode.