Rick, you might be interested in a book called "The Mood Cure" by Julia Ross. It was recommended to me by my naturopath.

Very briefly, it describes four "false moods" like depression, anxiety, the blahs etc., and describes the lack of serotonin, dopamine, and so on that causes them. And goes on to talk about the amino acids (protein building blocks) that these neuro-transmitters are made from, and how so many of us are lacking in them for various reasons. So if we're already short of dopamine, and then don't eat the substances that it's made from, we'd be really (unnecessarily) short.

I read this just before I went on holiday, and a few days of eating a lot more protein was making me feel a whole lot better. Then three weeks in Italy (with only a little protein every day) followed by a week of jet lag have undone any good. The next week should tell the tale.