I just stumbled over this article, which I wrote last year as part of an English writing/translation project. It belongs here on LD4all. 
Sleep Paralysis: annoying, maybe frightening, but harmless
You wake up in bed, only to find out that you can’t move. Not a single body part obey you, apart from your eyes. Your mind is partially clouded. Are you dreaming, have you been drugged, is something horribly wrong with your body? Something at the edge of your vision catches your attention. A tall, dark shadow stands between you and the window, slowly moving closer to your bed, not making a sound. You can’t take your eyes off this threatening vision, and you try to scream, but no sound comes out…
What is sleep paralysis?
If this sounds familiar to you, you have experienced sleep paralysis. The experience is most common immediately after waking up, and usually lasts for a few seconds. Because of the fear that can accompany sleep paralysis, those seconds can feel horribly long.
To understand what sleep paralysis is, we need to know a couple of things about sleep. Sleep is divided into several different phases: NREM 1, 2, 3, and REM. Every time we sleep, we cycle through those phases roughly once every 90 minutes. REM sleep is the phase where we usually dream. In this stage, the body (except the eyes) is completely paralysed. This is called REM atonia. If this paralysis didn’t occur, we would have acted out all our dream, and potentially injured ourselves. When we wake up quickly, and directly from REM sleep, consciousness may return before we regain control over our muscles. This causes conscious sleep paralysis.
Hallucinations in sleep paralysis
It is common to hallucinate in this state. The scientific word for hallucinations upon waking up is hypnopompic hallucinations. Several theories try to explain where these hallucinations come from; some say that they are a result of natural brain processes during sleep which imitate stress and fear reactions, and some say that they are simply background noise from the brain. A common hallucination is seeing, hearing or otherwise sensing an intruder in the bedroom. As soon as we wake fully, the hallucination dissolves. Seeing a dark, humanoid shadow is an especially common hallucination. I used to experience this often in my youth. Now, I usually hallucinate footsteps, the doorbell, or a cat curled up on my bed.
Simply knowing that this is a hallucination helps against the fear. It is good to know that this isn’t real, it is harmless, and will go away at least a few moments after muscles start working again. Most people experience this at some point. Some people experience it as much as once a week, and that can be a sign of an underlying sleep or anxiety disorder.
How do I get rid of it?
It is common to experience sleep paralysis more often if we are stressed or anxious. I have also heard stories of this happening after overuse of alcohol, tobacco, caffeine, or other psychoactive substances. Keeping a healthy sleep schedule and otherwise treating the body well may help prevent it.
Apart from the eyes and face, the first body parts to regain control are often fingers and toes. It can be effective to focus on them. When control comes back in a finger, the rest of the body should follow within moments. I have often made the mistake of focusing on my voice first, and that has just added more stress.
If the hallucinations aren’t too distracting, simply going back to sleep is also an option.
Sleep paralysis and lucid dreaming
It is possible to experience paralysis both while falling asleep and while waking up, even if the latter is far more common. For people who are familiar with the WILD technique, sleep paralysis can be used as an easy way into a lucid dream. The brain is already close to REM sleep. Some people have described how they simply roll out of bed, stand up, and find themselves in a fully formed lucid dream. It is probably a good idea to at least make it a habit to do a reality check after every sleep paralysis experience.
