A sound wakes you up in the night. You sense that you aren't alone anymore - something is there with you.
You rationalise: someone has come into your bedroom, that must have been what the sound was. Cautiously you turn your head to see if you can see them, but it doesn't move!
You panic.
The intruder is pushing down on your chest making it hard for you to breathe. You can't take a proper breath, let alone call out for help. You might just be able to make a slight sound in the back of your throat. You can't even move your head down to see who (or what) is crushing you.
There's a noise in the room too - ripping sounds, it's loud as if it's right in your ears. All sorts of thoughts race through your mind, before you pass out with fear. Then it's morning and all is well. There's no sign of intruders, no damage to your body.
What I've just described was an episode of Sleep Paralysis, and as scary as it is, it isn't harmful.
Most would class this as a strange night, and to be fair it is. However it actually happens to some people, and more accurately, it happens to me.
Folklore has many "explanations" for this, but they largely centre around applying cultural beliefs over the top of the facts. Explanations are as varied as:
Many cultures have their own name and culprit responsible for Sleep Paralysis, and a comprehensive list can be found here. A more modern piece of folklore about Sleep Paralysis is that it is an alien abduction and that the noises you hear whilst paralysed are actually medical experiments that are being conducted on you.
As the brain scrabbles to make sense of the situation it tends to fill in the gaps with dream-like hallucinations that are overlaid onto what you can see (remember that you have a fixed field of vision which is usually just your ceiling).
In fact in my first episode of sleep paralysis (I was 12 or 13 years old) I remember that as I was trying to scream I was also remembering stories that our house was haunted. So, the logical thing for me to think at the time was that this was an attack by some sort of ghost and that I wasn't allowed to see whatever ghosts get up to in the night, so I was being held down. (Yeah, yeah, yeah. I was 12).
A nice (and rather famous) depiction of sleep paralysis is a painting by Fuseli called "The Nighmare" in which a sleeper (sleeping on her back - which is frequently the position that paralysis occurs) is being crushed by a demon-like animal whilst a presence watches in the room.
The Nightmare by John Henry Fuseli, 1781
...although a more modern take on this painting might be something like this:
What's the real cause?
When we dream, our brains are as active (if not more active) as when we are awake. Our brain is generating fake sensory input and processing it as if it were real. The only thing that stops us getting out of bed and running around acting out our dreams is that the brain induces muscle paralysis during REM sleep, with only a few essentials left un-paralysed. This is called "REM Atonia".
Ideally this paralysis is activated at REM onset, and de-activated as REM stops. But sometimes it can come on too early or switch off too late, not only can this happen at the beggining and end of a REM period, but it can also happen during a REM period if the sleeper is briefly woken in what is called "an arousal".
Whichever way it occurs, effectively, the brain is awake and conscious but the body is asleep.
I was chatting with a friend who confessed that she is woken by spiders in her bedroom, dangling from the ceiling and spends a while trying to get away from them before waking up fully and realising that nothing is there.
After chatting I suggested that she put a familiar object in the room, so that if she saw it when an episode of this occurred then it would remind her that is was just a type of dream and she would be able to calm down. This seems to be different from Sleep Paralysis, and I doubt that she is aware of her surroundings in the same way, so it may not be of any use, but...
I then decided to have a go at that idea myself and purchased a large copy of Fuseli's "The Nightmare", had it framed and placed in on my bedroom wall so that I would see if when I woke up paralysed and remember what was going on.
One night I was repeatedly woken by my son's oximeter, I had to keep getting up and dealing with things and then get back to bed. Each time I got into bed I found myself paralysed. The first time I was scared, as normal but the picture helped calm me down... By the third time I found it funny. I recognised the familiar feeling that seemed as if someone was deflating my muscles one by one. I then thought to myself, "Okay, your body is alseep, but you are awake".
I calmly looked around the room and decided that I would get up. I thought to myself that if my body wasn't going to bother getting up, then I would get up without it, and no sooner had I thought that then there was a buzzing crackling tearing sound and I found myself about two feet above my body looking at the ceiling.
I then moved down towards the foot of the bed, my feet descended to the ground and I was free. I could look back at my own body (I only saw my feet still in bed). Just to the left of the foot of my bed was a figure. I knew that this was the presence that I'd felt whenever I'd had sleep paralysis, but this time I could see it!
Having never left my body before I was feeling rather pleased with myself. I looked at the figure and he gestured for me to go past him. I did, straight into (and through) a mirror into the room next door!
From that day I haven't been worried about sleep paralysis, in fact I've welcomed it. I don't seem to be able to easily reproduce the feeling of leaving my body (more often than not I hear the buzzing ripping sound and the excitement wakes me before I can "leave") but I can quite easily turn the experience into a lucid dream.
With the folklore around such powerful events, there seems to be a specific term for the presence I saw:The Guardian of The Threshold. It seems that his job is to intimidate you into not proceeding until you are deemed "ready". I guess that this is similar to hallucinations, emotions and images that meditators see, and claim that their purpose is stall the meditators into staying in that particular level of meditation.
However, for me, something seems to connect of Out of Body Experience and Lucid Dreams. It seems that I can't go through doorways in them, if I try to then I always end up somewhere else (usually on a high up place). I can go from room to room by walking through walls and mirrors easily enough, but for some reason never doors.
It's odd that now that I want it to happen more often, it seems to happen less frequently. Maybe the fear was a factor in causing it. What seems to happen is that as soon as I wake up and realise that I can't move I begin to think, "Right, let's see what we can do. Can I dream? Can I fill the room with dream imagery? Can I leave my body? etc". So the paralysis isn't the major event anymore, it's more of a gateway or a stepping stone.
Can anything help sleep paralysis?
Speaking from my own experience, there are a couple of things that you can do.
The majority of my episodes have ocurred whilst sleeping on my back (leading me to link them with apnoeas), although I have had some episodes whist on my side (oddly, with a side-lying OOBE "I" still left my body in the same manner - chest first, then a turn to face the ceiling, then moving towards the end of the bed, then feet on the ground).
So...