I imagine it like this. During the day, you are standing, you are sitting, you are walking. The thoughts that you often need the most have not yet grown strong enough to climb up through your tangled forest of lungs, and they slip repeatedly down, like a sediment made up of word and feeling and worry, probably to your stomach, where they settle as much as they can.
Then later, when you sleep, you are like a bottle of good wine tipped on its side; that sediment is now able to move, along your spine and maybe even towards your neck enough that you can start to feel it. Lying on your back in the half-light, in the dark, you become aware of the thoughts. They catch in your throat; the past and the future made from grit and sunlight.
Memories clearer than the water they were made in front of. Isn’t that how everything was meant to begin anyway? Islands carelessly dropped into the ocean, from a height so great that they can stay there.