Have you ever woken up unable to move, with a shadowy figure looming over you and filling you with immense terror? If so, you may suffer from something known as sleep paralysis – and you’re not alone.

Sleep paralysis is a little-understood condition that is thought to affect a range of people. It can last from seconds to minutes, and the experience can be extremely unnerving, enough so that people are afraid of shutting their eyes and going to sleep.

It usually occurs when a person is waking up or going to sleep. Their body will freeze, but they’ll feel a presence in the room – either seeing some sort of hallucination or just getting a sense of dread. This can range from a general feeling of horror to seeing an intimidating person in the room with you.

“The amount of times that I have felt that I was going to be murdered is astonishing,” Joey, 31, from Ohio, told IFLScience. “I get the sense that someone casually enters my condo. This person looms over me deciding whether to kill me or let me continue to sleep.”

Joey is not alone. Dozens of you sent your own stories in about your experiences, many with a common theme of fear and dread. Some people had only experienced sleep paralysis once in their life; for others, it was a living nightmare.

A study in 2011 of more than 36,000 people found that about 8 percent of the general population experience sleep paralysis at least once in their life. It was found to be more prevalent in students and psychiatric patients, with the study suggesting that “additional attention is warranted from researchers and clinicians alike.”

The UK National Health Service (NHS) says sleep paralysis is not harmful, but the experience itself can be extremely frightening. The main symptoms include being aware of your surroundings but unable to move or talk. Some people hallucinate, while others can move their eyes. Many report difficulty breathing and feel like their chest is being crushed.

It’s thought that sleep paralysis occurs when your deepest period of sleep, known as rapid eye movement (REM), is intercepted by periods of wakefulness. There is some sort of intrusion into wakefulness by some part of REM sleep, which is the reason you can remember the experiences so vividly.

“The experience of paralysis per se can be independent of the hallucination-like dreams that often occur,” said Professor Tore Nielsen from the Department of Psychiatry at the University of Montreal.

“Some people have the experience of muscle paralysis alone, even while seeming to be awake, and that can be terrifying enough. But the typical dreams of presence and other scary things can occur on top of the paralysis and maybe make the fear even worse.”

For most, the experience can be a one-off event, while others say it has occurred regularly over a number of years. If the latter is true for you, and it's affecting your ability to sleep, it’s recommended that you speak to your doctor. Although there are no direct cures, getting a regular six to eight hours sleep, keeping a stringent sleeping routine, and avoiding smoking or drinking alcohol before going to bed are said to be things that can help.

“I have had sleep paralysis [at least once a month] for over 15 years and I am in my 30s,” said Steve Graham, from Toronto in Canada. “For years it scared me but after reading about it I learned to control it somewhat, which can generally lead into lucid dreams.”

Like Steve, a lot of people who have had repeated sleep paralysis experiences say they have learned to control it, or even enjoy it. Many said that the more regularly it happened, the less traumatic the experience became – although that's certainly not the case for everyone.

Those initial experiences, and even regular events, can be terrifying. They can lead to a fear of going to sleep, as mentioned, and can cause some distress to partners who are unsure what to do when a person is suffering from sleep paralysis.

“It’s always a terrifying experience, every time,” said Trevor Elkins, 32, from Kansas City, Missouri. “I used to warn my friends at sleepovers to shake me if I was asleep with my eyes open when they woke up. No one has ever saved me though.”

 

The exact causes of sleep paralysis are not clear, although a lot of people report similar symptoms. Sleeping on your back seems to be a common cause, with people using techniques like sleeping against a wall or sticking a tennis ball to their back (with limited success) to stop them rolling over in their sleep.

Others have found that sleep paralysis is caused, at least in part, by sleep apnea – a disorder that causes your breathing to become interrupted while sleeping, for any of a number of reasons.

“It turns out my tonsils and uvula were huge, and were obstructing my breathing,” said Cindy Smith, 42, from New Orleans. “A month later, I had a UPPP (tonsillectomy, uvulectomy, and removal of excess throat tissue). I was a month shy of turning 40 by then. From the day I went home, my apnea and sleep paralysis were just gone.”

In the stories we heard, the experiences varied dramatically, from the general feeling of dread to believing there was an intruder in the room. Others have even reported experiencing alien abductions or witch attacks. The person usually realizes it wasn’t real after waking up, but that doesn't lessen the effect at the time.

“There was a tall dark figure standing next to the door and all I could hear was running water and a woman screaming, and it sounded like it was right next to my head,” said Nathan Weaver, 24, from South Wales.

“I tried calling out but nothing came out and I obviously couldn't move. It felt like it went on for ages, but was probably around 30 seconds.”

Sleep paralysis remains relatively understudied, but for many it is a horrible experience that occurs regularly. If you've experienced sleep paralysis, feel free to share your story below.