The definition of interstitial is ‘in-between.’ Something can be deemed to be ‘interstitial’ if it exists within a space that lies between something else.
We are in such a ‘space’/an interstitial zone of consciousness, when we are neither fully awake nor fully asleep (e.g., when we are ‘drifting’ off to sleep, unresponsive but still able to hear sounds in our immediate environment, or when we are slowly awakening from sleep.) These two states have scientific names, with these names being ‘Hypnagogia’ (the state of consciousness between wakefulness and sleep) and the opposite of Hypnagogia, ‘Hypnopompia’, (the state of consciousness leading out of sleep- between sleep and wakefulness.)
It is during these interstitial zones of consciousness, whether that be prior to fully falling asleep, or prior to fully awakening, that our bodies undergo noticeable changes, namely that; our brain activity slows, our muscles relax, and our sense of reality gradually distorts.
Often referred to as a ‘meditative’ state, many people claim that being in the interstitial zone provides them with an opportunity for greater creativity to occur. In fact, Famous American Inventor Thomas Edison, and Spanish Artist Salvador Dali, took this opportunity for embracing creativity one step further, by devising methods for recording the ideas that would come into fruition in this state of consciousness. One such method involved them taking naps whilst holding an object specifically chosen for the noise it would make when dropped. The idea behind this was that, just before falling asleep, Edison and Dali would drop the object which would subsequently awaken them, therefore allowing them to record the creative ideas they had when they were drifting off, something which otherwise might have been impossible for them to do, a result of many people forgetting what ideas come into their head prior to them falling fully asleep.
‘When we enter sleep, the brain steadily dismantles the models and concepts we use to interpret the world, leading to moments of experience unconstrained by our usual mental filters.’
You enter the same interstitial zone as described above, or at least, a very similar one, when you engage in meditation, too, whether that be of the more ‘traditional’ sitting down, eyes shut kind, or the more ‘unconventional’ form (e.g., via exercise, art, etc…)
Ultimately then, it can be said that anything which causes one to forget about the day-to-day complexities of life and forces them to just live ‘in the moment’ is, ultimately, a gateway into the ‘interstitial zone of consciousness.’