Between wakefulness and sleep is a fascinating, hallucinogenic state of consciousness that you’ve likely experienced even if you didn’t know it had a name. It’s called hypnagogia, and during this brief transition you may feel unusual sensations, see splashes of color, streaks of light or other visions. Or perhaps come to a brand of existential insight normally left to acid trips. It's a perplexing state, one that has inspired creativity and confusion to equal measure. And it can lead to some of our most unique thoughts. 

The term hypnagogia derives from the Greek words hypnos, meaning sleep, and agogeus, meaning guide, or leader. The altered state may last just a few seconds or several minutes. In it, you’re neither dreaming nor fully unconscious, yet you have enough self-awareness to catch your thoughts drifting as you’re slowly “led” to sleep.

What does the leading are brainwaves. Fully awake, our brains emits beta waves, which are characterized by active thinking and focus. These are good for problem-solving, but they can also bring on anxiety and stress. In a relaxed state, your brain produces alpha waves, and just before REM sleep, we shift to theta. Hypnagogia is marked by presence of both alpha and theta brainwaves. And it’s this unique neural synergy that creates the state of “threshold consciousness,” where we feel as though we’re straddling the waking and dreaming worlds.

As our brain waves vacillate, we begin to lose our so-called ego boundaries and our awareness becomes less logical and linear. We’re more open, empathic and suggestible to outside and other influences. When our brain’s empirical left hemisphere loses sway, fluid association between ideas, thoughts, images, feelings flow more easily; without the normal constrictions of logic, we can experience extraordinarily inspired and creative moments.

Hypnagogia has probably existed as long as humans. But, as Neel Patel discussed at length in his piece "Sleeping on and Dreaming Up a Solution" Scienceline, scientists have only been formally studying it since 1987 when the psychologist Andreas Mavromatis published the first important paper on it. .

Edgar Allen Poe, for example, wrote of so-called fancies that he experienced “only when I am on the brink of sleep, with the consciousness that I am so.” Mary Shelley, as Patel pointed out, claimed that her masterpiece, Frankenstein, was inspired by a “waking dream” that she had while falling asleep.

Hypnagogia researcher Deirdre Barrett, Ph.D., a clinical psychologist at Harvard Medical School, notes that Thomas Edison and Salvador Dali both had methods of deliberately instigating hypnagogic dreams. Edison would hold a set of metal balls as he napped, and when his hand relaxed, the balls would crash to floor. Waking with a start, he usually had a solution in mind.

Whether you try to consciously create or tap into this state, or simply enjoy its drifty, trippy sensations, Patel points out that consciousness researcher Marques-Bonham, from the University of Texas at Austin, notes that “hypnagogia is the shortest path for communication from our subconscious. Your subconscious mind might send you solutions through imagery or other sensations,” she says, likening this to Archimedes’ famed “Eureka!” epiphany.

In addition to inspiration and insightful visions, hypnagogia brings auditory hallucinations as well. It’s not uncommon for people to hear voices, doorbells or even music, some of which is loud enough to wake them. Occasionally there are smells or some type of touch. This is believed to be what happens naturally when the brain goes into a state of sensory deprivation.

Another phenomenon that occurs during hypnagogia is sleep paralysis, the curious condition of being barely awake yet unable move while still experiencing dreamlike visuals and feelings. While this can be distressing, scientists believe it exists for our safety. Without this protection, we might try to physically act out what we’re dreaming and possibly injure ourselves—or anyone else who’s around. And in the weird world of hypnagogia, that could get freaky.  

This article has been updated to cite Neel V. Patel's article "Sleeping on, and Dreaming up, a Solution" on Scienceline.