Have you ever wondered how people sleep walk? Well normally, we don't act out our dreams because a mechanism in our nervous system paralyzes our body when we're dreaming. But if for some reason that mechanism doesn't work on cue, then if a person dreams, that person will act out that dream and sleep walk.
Hopefully that little example will give you a context for what this page is about. It explains the direct causes of sleep paralysis, hyponogogic hallucination, and lucid dreaming. Sleep paralysis is when you are unable to move after waking up or before going to sleep. Hypnogogic hallucination is when you hallucinate after waking up or before going to sleep. Lucid dreaming is when you are aware that you're dreaming.
The Experience Systems
The following table shows the experience that results when each of the main three systems is either on or off (memory is considered later):
The normal cycle of experience you go through is normal waking, normal sleeping, normal dreaming, normal sleeping, then normal waking again. To achieve this, the three systems have to be turned on and off in a synchronized way. If they aren't, an abnormal experience results.
For example, suppose you are dreaming and then wake up. Now, if your paralysis system doesn't turn off right away, you will be lying there in bed, awake, but paralyzed. That is sleep paralysis. On the other hand, if your dreaming system doesn't turn off right away, you will continue to see and hear your dream even though you are awake. That is hypnogogic hallucination.
Perhaps the most frightening case is when both your paralysis and dreaming systems fail to turn off. Then you are lying in bed awake, but paralyzed and hallucinating. This is hallucinating paralysis, and is theorized to be the real cause of what some people call alien abductions.
Often people report that when they hallucinate after waking up they hear a loud tone, squealing, or static. This is likely the result of feedback loops in the hearing nervous subsystem. It is akin to hooking two incompatible inputs into a stereo speaker.
The Memory System
I've not yet mentioned the two states highlighted in blue. A disorientation fugue (my term) is when you're awake but can't remember what's happening, where you're at, or why you're there. Aware sleep is when you're asleep and not dreaming, but still somehow aware of the passage of time and of the fact that you're sleeping.
The above analysis has been dispassionate to the fact that sleep paralysis and hallucinating paralysis are extremely frightening experiences. Hopefully, with the above knowledge, your next, or first, experience of these will be less a fright and more a fascination.