What is hunger?

Another post based on a note from a couple of weeks ago ....

I'm trying to understand what hunger is all about?  OK, that sounds crazy or pretentious, so let me explain what I mean.

A couple weeks ago I had to get some blood drawn for my routine physical, and that meant a 12-hour fast the night before.  I did it, and found that it wasn't terribly arduous.  So then I thought ... well hey, maybe I can do this more often.  If I skip one meal a day -- dinner, for instance -- then maybe I'll stop steadily getting fatter the way I've been doing lately.  The next night I tried that and succeeded, more or less fine.  But I couldn't sustain it longer than that.  The next night I had to have something to eat in the evening.

What is so interesting to me is that I didn't exactly feel hungry, not in the sense of my stomach feeling empty or hurting or growling.  Nothing like that at all.  As far as physical discomfort was concerned, I could have skipped dinner all week long.  It's just that I felt ... strange.  I don't know how else to put it.  Something felt wrong about not sitting down to some food in the evening.

I still don't really understand why.