I have a friend who is a really nice guy. The problem is that he was born as a half demon. While he looks completely normal, he possesses a spirit inside him called "Amon". This being forces him to experience certain demonic urges, which he must constantly suppress while awake.
When my friend falls asleep, he loses control of his body to Amon. The demon must wait for him to fall into his REM cycle, which is the deepest mode of sleep in which the human begins to dream and will not be easily awakened. During this time, my friend becomes possessed and gains his demonic abilities, such as super strength, speed, durability, and power of flight. The demon then goes out to do horrible things and commit murder and mayhem. When cornered by this creature one night, I asked this creature what it's name was, and it's response was that "I AM.....DEVILMAN".
REM sleep is supposed to be the cycle in which your muscles are paralyzed, which prevents your body from moving. This is intentional as to stop you from acting out your dreams, and should prevent an evil spirit from taking you over. How is it that Amon is able to bypass this human drawback created by millions of years of evolution?