I might be completely off the mark … but my guess is … you are looking at the reflection of your eye so you are focussing on a fixed point … if you move your head left or right and keep looking at that fixed point … your eyes will seemingly rotate within your head. Similarly - tilting your head back with your eyes focussed on the fixed point of the reflection - your eyes roll forward - giving the illusion of your eyelids closing - but really - it’s just your pupils are looking out of the bottom bit of your eye socket? instead of the middle.
If - with your head now tilted upwards - you stop focussing on the reflection of your eyes and look straight ahead (i.e. at the ceiling) - your eyelids don’t move … ergo … eyelids weren’t responding to gravity.
I think Mr C has it as that was going to be my explanation. I don’t think gravity has anything to do with it. (Perhaps the specific gravity of the alcohol you consumed has more to do with your results?)