The classic definition for this phenomenon is called sleep paralysis. The strange phenomena is actually not uncommon. Those who experience it suggests, "..it lasts a few seconds, several moments at most, or occasionally longer and usually occurs right before you are about to fall asleep or wake up."
Many have reported that when experiencing sleep paralysis, they feel a “presence” of something often described as "malevolent, threatening or, evil," and many feel a tremendous amount of terror and panic. Scientific approaches although assert the phenomenon of experiencing sleep paralysis is simply one of hallucination
There are examples of the phenomenon that would fit under the umbrella of “spiritual” ideas, such as the sensation of floating or being outside the body, or visits from entities not of this world, near death experiences, and more. Outside of spiritual philosophies, quantum science has shown us, there are "worlds within our world that we are not able to perceive easily yet," AND perhaps the experience of sleep paralysis may be one.
Could the phenomenon of sleep paralysis be related to what's known as lucid dreaming, as individuals report being conscious during a paralysis state while in bed? Lucid dreaming is when one experiences a dream state while being totally conscious of it. Tibetan Buddhists are known to practice lucid dreaming as a means of approaching enlightenment. Basically they strive to control their consciousness while dreaming.
The nature of sleep paralysis is no doubt intriguing and real for many individuals of sound mind. Those in the scientific world who dismiss the experience as completely false while not having facts to identify the phenomenon as such would perhaps be better to place it in the realm of neutrality, and as being a phenomena unexplained.