These past few weeks I was working on a pretty serious and involved assignment, but I felt very calm.
For me that's a major change because I have problems. I have problems with depression, I have been suicidal in the past, I tend to be anxious, I also am hot-tempered and have anger problems...not violent ones, but just all the features of your classic "type-A" - neuroticism, perfectionism, free-floating hostility.
So, yeah, I've definitely noticed I seem to be in a better mindset since going Primal.
I had noticed exactly the same things OP describes.
I used to feel anxiety quite often. When I started I was eating pretty much VLC all the time. Later on switched to LC and now I'm kind of low to moderate on the carbs (in the context of CW). Still have the same sense of well being and calmness, no matter what.
I have come to the conclusion that it's all due to the change in diet, maybe the elimination of grains? Not sure, but I certainly like it.
This was my first thought about the mechanism, but I'm sure it's part of the deal at most:
Effects of food contentIn humans, serotonin levels are affected by diet. An increase in the ratio of tryptophan to phenylalanine and leucine will increase serotonin levels. Fruits with a good ratio include dates, papayas and bananas. Foods with a lower ratio inhibit the production of serotonin. Research also suggests eating a diet rich in carbohydrates and low in protein will increase serotonin by secreting insulin, which helps in amino acid competition. However, increasing insulin for a long period may trigger the onset of insulin resistance, obesity, type 2 diabetes, and lower serotonin levels. Muscles use many of the amino acids except tryptophan, allowing more muscular individuals to produce more serotonin. Myoinositol, a carbocyclic polyol present in many foods, is known to play a role in serotonin modulation.
 In the digestive tract (emetic)[/quote]
I've always been a pretty mellow guy, but now I'm really mellow. I take a pretty relaxed approach to everything and just deal with life as it happens. With that being said, when the stress gets to be too much and I do fly off the handle, I REALLY FLY OFF THE FUCKING HANDLE! It doesn't happen very often at all, but it scares the hell out of my family, which scares the hell out of me.
I experienced the same points you did.[img]http://www.usa-nfl-houstontexans.info/21.jpg[/img]
Gluten has a horrendous effect on my mental health - I have celiac disease, so this may not be true for most people - but I feel like a crazy person if I accidentally eat it. Anxious, depressed, angry, irritable, etc. - and much LESS tolerance for things like loud noises and strong smells. Eating gluten free was a great first step for me, but I'm feeling even better now that I've cut out processed food, sugar and alcohol. What you eat can definitely affect your mood and your mental health and your perception of stimuli.