A bit of a follow-up: some recent blood work, web searching and reading has caused me to experiment with supplementing with tyrosine.
http://www.umm.edu/altmed/articles/tyrosine-000329.htm
Recent blood work indicated that my TSH was borderline high but my thyroid hormones were borderline low, suggesting a deficiency in the precursors (tyrosine or iodine). I had been running cold, low energy, etc. and have a family history of thyroid issues so I had those levels checked. Also, several years ago I was diagnosed with seasonal affective disorder and was put on a course of Wellbutrin (buproprion) which is a dopamine-reuptake inhibitor. I responded well to it, but after a time I decided that I did not want to be on meds and discontinued their use. Supplementing with vitamin D helped somewhat during the winter, but I read that tyrosine is a precursor to dopamine. It seemed that tyrosine was a common factor in all these issues, so I decided to try supplementing with it.
I've been on tyrosine for two weeks and must say it has brought about a night-and-day difference in mood, even while in deep ketosis and exercising hard in the middle of winter. I'm warm now, energy and enthusiasm are both good, and I am finally seeing exercise as a joy instead of a chore.
I'm continuing on the supplements for now, but tyrosine is an amino acid found in meats, eggs, dairy, nuts and wheat, so in theory I should be able to get a sufficiency through food. I think the problem may have been that I was restricting too much and pushing too hard while not eating enough meat and eggs to fill a chronic tyrosine deficiency. I think I will remain on the supplements while I am still trying to lose weight and then try to phase them out when I reach maintenance.
Tyrosine is apparently something that has been known about by bodybuilders trying to cut:
http://www.bodybuilding.com/fun/tyrosine.htm