Last night I awoke with my head under the covers, to the sounds of strange chitterings and scratchings in the darkness around me. For a few seconds I lay frozen, hoping the sounds would fade – but they only grew louder and drew nearer – until at last, unable to stand it any longer, I threw aside my blankets to confront them.
But the instant I moved, a hideous roar shook the room around me and I felt the blankets thrown over my face, plunging me into suffocating blackness. A wave of primeval fear gripped every nerve in my body, and as I tried to escape I found that my limbs no longer obeyed me – I was paralyzed, trapped beneath overpowering weight, unable even to release the screams that clawed up my throat-
And I woke again – into the real world, this time. I hurled my blankets from me as I lay panting, trembling, my body soaked in clammy sweat. In the sudden clarity of my adrenergic awakening, it took me only a moment to realize what I’d just experienced: sleep paralysis and hypnagogic hallucinations – neither of which had afflicted me since I was a young child. Nor – despite my generally adventurous temperament – am I eager for a repeat performance anytime soon.
Sleep paralysis and dreams – along with nightmares and their less-common cousins, night terrors – belong to a class of experience many of us dismiss as somehow “unreal,” or at least “less real” than the world we experience in waking life. But for most of human history, these occurrences were regarded with deadly seriousness, as clear evidence of invisible evil forces lurking all around us. In some cultures today, they’re still regarded as visits from the Old Hag, a mysterious visitor in the night.
Underlying many of these discoveries is a growing realization that the boundary between waking and dreaming isn’t nearly as clear-cut as we might like to think. For example, most of us have heard of lucid dreams (dreams in which we’re aware we’re dreaming) but less well known are hypnagogic hallucinations: perceptions that blend sensory input with dream data, and feel like they’re part of waking consciousness. Hypnagogic hallucinations can involve visual, auditory and tactile sensations – and some who experience them even report that they seem more vivid than the waking world does. Mine certainly felt real enough.
And so we arrive at the strange world of parasomnia – disorders that blur the lines between sleep and wakefulness.
One of the most common parasomnia disorders – sleep paralysis – is often a companion of hypnagogic hallucinations. Simply put, it’s a semi-wakeful state in which one feels conscious but unable to move. As it turns out, though, sleep paralysis is a byproduct of the body’s natural journey from wakefulness to sleep.
Each night, as our brain switches over to REM sleep mode, certain areas of the brainstem – especially the pontine tegmentum – send out signals that trigger a state known as REM atonia: a paralysis in which neural signals destined for motor neurons are blocked from reaching their destinations.
It’s a good thing our brains can generate REM atonia – because without it, we’d all be flailing around our bedrooms every night, acting out the scenes in our dreams. We know this because researchers have blocked the process of REM atonia in experimental animals, and found that these animals don’t just sleepwalk – they mime all sorts of experiences, from hunting to fleeing predators, as they sleep.
Night terrors – attacks of intense dread that often cause children to sit bolt-upright, eyes wide open, and even flee across the room – seem to be cases in which the body’s fear-response instincts override the neural inhibition imposed by REM atonia. Luckily, night terrors are far less common in grown-ups than in children – though anxiety-prone adults have been known to experience them.
What’s even more intriguing, though, is that, through research with drugs like scopolamine and zolpidem, researchers can artificially induce states of consciousness that blur the boundaries between sleep and wakefulness still further. While asleep, patients on zolpidem have been known to prepare and eat food, to have bizarre conversations, to try to drive vehicles and even to initiate sex. Meanwhile, scopolamine can trigger hallucinations that sound strikingly similar to hypnagogic ones – and it can induce “zombie-like” states of consciousness in which patients respond to direct questions and react to bright lights, but don’t appear to be otherwise conscious of the world around them (or to remember the experience afterward).
Studies like these demonstrate that consciousness isn’t really a waking or dreaming phenomenon – or even necessarily one discrete phenomenon at all. Instead, it seems to be a somewhat modular method for organizing information about the world, and preparing responses to it – whether that world is a physical one or a mental one. And as examples like these show, that distinction isn’t always a clear one.
If you’ve been suffering from sleep paralysis or night terrors, you might consider visiting a therapist, or at least taking up yoga or meditation, because anxiety is one of the most common causes. But whether you’ve experienced these strange phenomena or not, they serve as eerie reminders of the complex neural dance that underlies our conscious awareness, our experience in our bodies, and our sense of presence in the world.
What I’m trying to say is, consciousness is a fragile, precious, extraordinary thing – so be careful with yours.