Biology behind sleepiness and eye behavior

Factual Questions
1

Because I forgot to take my daily stimulant, it was post-lunchtime, and it was a boring meeting, I started to get really really sleepy yesterday.

My brain didn’t really feel that tired, but my eyes, oh my eyes. If I wasn’t focusing on looking attentive at that very moment, I would get brief segments of time (seconds) where my vision would go all wonk. My eyes kind of wander off and I see double vision. Or the world will blur out of focus. If I don’t pay very close attention my eyelids may essentially close involuntarily.

What is the biology behind this sleepiness-eye malfunctioning connection? Why can’t I be sleepy and not have my eyes go all bonkers. Why don’t my ear functions do strange things?

I am guessing my brain is releasing some chemical that tells my eyes to just not pay that much attention to the conscious me anymore?

2

I don’t think it’s an ‘eye thing’…you were falling asleep. It would probably be cool to see an EEG of that moment.

3

Because processing imagery is HARD work (just ask any programmer). It’s a bit easier with specialized pre-processing neurons, but it’s still a lot of data for your brain to process.

Also, your eyes are constantly adjusting: changing focus as you look at different distances, contracting your pupils as the light hitting your eyes changes (which happens every time your gaze moves toward or away from a light source)

4

Sort of. What I was getting at was that my head didn’t droop. My hearing didn’t fade out. Eyes seem to bear the brunt of the “shutting down.” Why is that? What tells them that they don’t have to act properly anymore?