Paradoxical sleep is also called activated sleep, deep sleep, desynchronized sleep, rapid eye movement or REM sleep, para sleep, and rhombencephalic sleep. This sleep state is also known as dreaming sleep or D-state since it is nearly entirely devoted to dreaming. Your brain is extremely active during paradoxical sleep, and your eyes move in a quick, back-and-forth motion rather than the slower, rolling motion that happens during other phases of sleep. Your muscles, on the other hand, are nearly completely paralysed, despite the fact that your eyes are moving a lot and your brain is busy.
What is so paradoxical about it? Well, you are awake and asleep at the same time, thus the paradox. You’re sleeping, yet your brain is working and your muscles are resting. This is the sleep when people often dream, have sleep paralysis and have nightmares and more. One of the two main sleep stages, paradoxical sleep, is distinguished by the presence of fast eye movements (REM).
To govern the transitions between waking and sleep, the brain stem, located at the base of the brain, communicates with the hypothalamus. (The pons, medulla, and midbrain are all parts of the brain stem.) GABA is a brain neurotransmitter produced by sleep-promoting cells in the hypothalamus and brain stem that serves to lower the activity of arousal centres in the hypothalamus and brainstem. In REM sleep (paradoxical sleep), the brain stem (particularly the pons and medulla) sends messages to muscles important for body posture and limb movements to relax, preventing us from acting out our dreams.
People who have issues in this mechanism often sleepwalk. While on the other spectrum of this is sleep paralysis. A typical REM sleep cycle includes intense dreaming as well as atonia, which prevents dream actors from carrying out their fantasies. Atonia ceases when a person wakes up, thus the inability to move is never noticed. A mixed state of awareness including alertness and REM sleep is known as sleep paralysis. In fact, the atonia and mental imagery associated with REM sleep appear to remain even while the person is awake and conscious.