I guess I should say “Sit up and pay attention while I answer your question!”
:-)
I certainly do, from personal experience. About 5 years ago, I was working at a high-tech company in Silicon Valley and found that the only way I could focus on my work was to have a stand-up workstation, which kept me from slouching in my comfy chair and turning into a web-surfing distraction-seeker.
This is why teachers tell us “sit up and pay attention”: certain postures, such as laying down or even slouching in a chair, seem to trigger certain states of mind, such as sleepiness or just plain relaxation, rather than alertness.
Medical research into the relationship between posture and alertness and productivity continues. You have probably heard over and over again that we have five senses: sight, hearing, taste, smell and touch. In fact, we have far more senses, generally grouped into two categories: ”exteroception”, which deals with sensing things outside our bodies (the five senses above, plus the sense of balance) and ”interoception”, which deals with sensing things inside our bodies (pain, hunger, thirst, and so forth). About a hundred years ago, though, scientists described ”proprioception” (“the sense of one’s self”), which deals with awareness of how your limbs and body are positioned—whether your arm is outstretched, where your right foot is right now, and so forth.
With no specific scientific knowledge to back it up, forgive me, I suspect that some combination of the senses of balance and proprioception are involved in helping us fall asleep, wake up, be prepared for challenges. I also suspect that we developed those senses and that unconscious relationship among them through evolutionary adaptation (I wouldn’t call it a throwback, but a useful adaptation, like the ability to feel pain, which can save our lives.)
I hope this helps.