How is it that I can go to bed really, really hungry....like I could eat a 6" sub sandwich it two bites...but I wake up in the morning not hungry at all?

Probably some fat got burned up for energy and you got gassy and your metabolism slows down while you sleep.
But actually there was a study done that the scent of food and seeing it for a few minutes actually can reduce hunger pangs and convince your body you are full.
I agree with this, because I have been really hungry sometimes while cooking and not even have a bite and find after cooking for more than an hour, I am no longer so hungry. I’ll have a few bites instead of a full plate.
When I worked in food establishments it was the same. I ate very little and always felt full. It was easy for me to avoid eating a lot or snacking.

I think it has to do with being hungry for the wrong reasons maybe? I have a similar thing happen to me where I’m hungry and want to eat more, and then three hours later having not eaten anything I’m just fine.