Thinking, and even the body's reactions, transcend time, or at least don't follow the perception (illusion?) of time traveling forward with a fixed and unchanging result. It was something I too came across unexpectedly in a simple personal sleep experiment, and then again at different times in various writings or other official experiments that had nothing to do with parapsychology to begin with.
It is normal to be able to do different things at the same time, so long as the various tasks are well-primed in memory and routine enough. The "executive" can then supervise these tasks, switching between them as necessary, or work on new information as it enters working memory, at least up to the point where it runs out of resources (mainly, working memory capacity).
Those who've researched trance outside of the mainstream proposed a wild theory that this increase of 'psychic energy' is made available as various cognitive centers are 'shut down.' From here, the theory can expand endlessly to try and describe how or why this happens. Is it the brain hemispheres working together to help channel greater parts of the subconscious? Is it the lower brainwaves, or their inversion into highly coherent peaks, contributing?
What's more important I think is that it works, and that meditation, mantras, prayer, manifesting, siddhis, etc. are put to use to amplify their effects given what's already known. It might mean losing out on the 'why and how,' including how to make it more efficient, but I think it makes more sense to apply what's already been discovered, than to stall early on to figure out why. In this way, new inner resources will emerge that add much more to the understanding afterwards, something that would be entirely unforeseeable and inaccessible otherwise.
About what is happening when the mind is quiet, I believe that is the description of dhyana, meditation, the process of sustained application of a technique in leading or giving way to the next stage, samadhi.
