Sleep occurs in regulated cycles of NREM and REM. For every 90 minutes of sleep, we drift into stages of NREM and REM: N1 -> N2 -> N3 -> N2 -> REM. During REM sleep, the body is paralysed, except for shallow breathing and eye movements. For most of us, REM stage occurs ninety minutes or so after falling asleep.
However, people with narcolepsy or sleep deprivation may fall into REM at the very start of sleep, plunging into dreaming and sleep paralysis. They may also wake at the “wrong” time, so that the dreamlike visions and the loss of muscle control persist into the waking state. At this stage, the person is wide awake but suffers from nightmare like hallucinations and be unable to move or speak. These hallucinations may be visceral, auditory or tactile as well as visual and are accompanied by a feeling of suffocation or pressure on the chest, the sense of a malignant presence, and an overall sense of absolute helplessness and abject terror.
Yet one need not have to have narcolepsy to experience sleep paralysis with hallucinations. Research has shown that about a third and half of the general population has had at least occasional episodes of this. In fact, folklore across cultures share a common experience: supernatural figures that assault the sleeper, some paralysing the victim and even sucking away his soul. While these frightful experiences have led many to believe in supernatural forces, there is in fact a physiological basis for this occurrence. Where our minds fail to comprehend, we can always look to science.
For me, I have had an experience of awakened consciousness in sleep, accompanied with bodily movements. On 25 August 2013, I woke mid-sleep at what may have been 3am. I found myself scratching my legs and told myself to stop. Yet, I knew I could not will myself to do so. I even mused to myself, as if one half of my brain was talking to the other, as I observed my bodily movements. I heard sounds as I made them. Then, I got off the bed and made my way to the washroom. As I sat on the toilet seat, I heard myself hum a tune. I found it funny that I was humming, and yet I knew I could not will myself to stop. I do not know if I saw myself in the mirror, or how I made my way back to bed. Yet, all these observations were remembered clearly when I woke fully the next day. It impressed upon me that we know so little about our consciousness, about our minds. It was an unforgettable experience. I never had the same experience since then.
Nevertheless, there were several times I woke to realise that I had sent a message mid-sleep, with absolutely no recollection of having unlocked the phone, and sending one. It would seem right to say that I had sent a message unconsciously, but that offends logic. It would then seem appropriate to say that I sent it subconsciously, while asleep.
Sleep, dreams, our consciousness and our minds continually interest me over the years and this curiosity will never be satiated.
For more information on narcolepsy (and cataplexy), hallucinations and sleep paralysis, do read Hallucinations by Oliver Sacks.