This painting:
is known as The Nightmare and was painted in 1781 by Henry Fuseli. The image is representative of what it is like to have a waking dream. Waking dreams can be related to, but are not necessarily the same as, lucid dreaming. While lucid dreaming, the dreamer is supposed to be able to control the dream. He or she is in a state of being aware enough to realize that they are dreaming and can make decisions regarding the dream, but not aware enough to wake him or herself up. A waking dream involves waking up in a panic, feeling paralyzed, and often sensing something sitting on your chest or in the room with you. More often than not, this "presence" is perceived as malevolent. I had one waking dream back in high school and that was enough.
The reason people experiencing waking dreams feel paralyzed is because they are paralyzed. After we fall asleep, our muscles are paralyzed so we can't hurt ourselves too much. During a waking dream, we regain consciousness without regaining motion in our limbs. I wonder if this is the opposite of sleep walking, in which we regain control of our body, but our mind doesn't wake up. I'll have to look into it.
With your muscles somewhat stuck, it's more difficult to breathe than usual. People used to believe that some spirit or creature was sitting on the chest of the dreamer, as seen in The Nightmare. It is pretty easy to make the jump from "I've been paralyzed and I can't breathe" to "there is something trying to hurt me."
In fact, this may be how people end up believing they've been visited, or even abducted, by aliens. Culture plays a large part in the appearance people give their visions. Centuries ago, the presence was thought to be a spirit or witch. Now aliens are more popular. The most common type of alien abductions reported change over the decades as pop culture descriptions of aliens and UFOs change too.
Stress is supposed to be a cause of waking dreams and sleep paralysis, as is sleep deprivation, so I think I will go to bed now. Good night!
