apropos of nothing, have you ever tried to actually get your jaws around someone else's head? you can't really open your mouth enough to do more than scrape the skin - biting someone's skull open would probably not be possible.
I'm a hobbyist gardener - or, rather, plant enthusiast - but even if I know that the plants themselves might be considered valuable, the scale I'd have to engage in it to make it capable of supporting me in its own is... daunting, to say the least.
I would guess this effect is caused by lowered anxiety, or rather, reduced alertness. I take a medication that includes an adrenal blocker - for my anxiety - and if I miss even a day my dreams go crazy as my body is flooded with levels of adrenaline it's no longer used to.
I think most species probably align themselves to either the galactic plane or prominent orbital plane of the local star system.
the "up" & "down" directions would be completely arbitrary, though. there's no reason to think everone would decide on a standard for those.
and species without that certain sense of appropriateness, or an overt dedication to logic, would likely not bother with a standard orientation. and especially when in orbit over a planet, I think everyone would orient their "down" towards the surface.