As I often do when I’m beginning a new essay, I seek out the etymology of the word I want to explore. This time, I’m disappointed that the word “nightmare” has nothing to do with horses. The idea of bad dreams as horses galloping through our night-time hours resonates with me.

But mare comes from the old English maere , the word for a goblin who sits on a sleeper’s chest – a succubus. The Nightmare , the famous 1781 painting by Swiss painter Henry Fuseli, hedges its bets, depicting a squat gargoyle-like figure crouched on a swooning maiden, with a donkey-ish horse looking on from the shadows. Though called The Nightmare, the experience depicted is more akin to sleep paralysis, that strange phenomenon where we wake up unable to move.

I’ve experienced this several times – waking with a shrill buzzing in my ears and panic rising as I realise I’m boxed in, a mind trapped in an unresponsive body. But nightmares are a broader spectrum of experience. They can be full of stock horror-film tropes we’ve absorbed from the world around us, or troubling, uncanny images that spark terror in us as individuals, but are otherwise untranslatable.

My earliest memory of a recurring nightmare was terrifying precisely because it was devoid of images, and seemed fuelled by a deeper knowing that had no access to the conscious level of thinking that translates sensation into meaning. For the purposes of writing about it, I have to translate the ideas in the dream into images, but .