Explain really tired phenomena

Factual Questions
1

Why do certain things happen when you get really, really tired? Like right now, I’m really tired.

Why, when I’m really tired, do my eyes go cross-eyed and googly and it becomes quite an effort to keep them looking straight?

Why, when I’m really tired, do I constantly think I see things out of the corner of my eye, causing me to look to my side and find that there is in fact nothing there?

Why, when I’m really tired, do I get giggly and find things that aren’t funny funny? In other words, “slaphappy”.

Why, when I’m really, really tired, do I eventually get a second wind that rejuvenates me for an hour and I return to a somewhat normal state, before falling back into a cycle of fatigue and sleepiness?

2

You were probably born with a certain amount of stabismus, but not enough to require ophthamological correction, and all your life you are unconsciously accommodating it by using your eye muscles to un-cross them. When you are tired, your muscles relax, and you notice that your eyes are crossing.

I also find that if I totally relax my eyes, they fall into a slightly crossed configuration.