People tend to not like lifestyle answers, but I've always found the problem is usually right in front of you:
I know when I'm sitting calmly, busting out witty yet insightful prose to calm the anxious drug users of the internet, and a sense of impending doom overtakes me, with a cold sweat, legs suddenly shaky--I check my blood sugar. Actually I usually just run for a bunch of Smarties and don't bother checking. When I do, it'll be around 50 g/dL. So low blood sugar is definitely a cause of anxiety, or probably more accurately, rapidly falling blood sugar (if it's slow it's more like drifting into a blissful dreamlike state, and you just . . . stop). That anxiety is from adrenaline released to force sugar out of your liver.
That can be reactive too, so that hyperinsulinemia after a meal triggers a sudden drop in sugar, even though you just ate. I used to feel that like ten minutes after some meals--the will to live just draining out of me. That was twenty years ago when I still made insulin.
High sugar is not as bad, but still anxiety-provoking. I figure that might be the acidosis that goes with it, since low blood pH is a potent trigger for anxiety. High blood sugar is obv. more chronic and easy to miss. General discomfort, a feeling like you're not quite getting enough air, a little agitated, annoyed, confused, and mild anxiety. You're tired but antsy, want to get out but also to just lay down.
It can come on a couple hours after you eat, so "simply eating" could be missed as a factor pretty easily. If you fast for bloodwork, it might not show up if you're in early diabetes stages or don't regularly eat big meals. In other words, I knew something was wrong, and adjusted my diet, and even though it turned out I'd been diabetic for years, I wouldn't have shown high fasting glucose. I needed some ice cream and a meter (up to 400mg/dL) to convince myself and the doc to get an A1C.
I'd like to point out I developed diabetes as a skinny, active teenager, saw it through a big weight gain in my twenties, back down to a skinny guy now. You don't need to be even overweight to get it.
All it takes to find out is your doctor taking an A1C measure, just a blood draw. It measures glycosylated hemoglobin. Blood glucose in its linear aldehyde form reacts randomly (as aldehydes do) to hemoglobin, and since the life of an RBC is about eight weeks, it serves as a kind of average blood sugar level.
It may not apply to you OP, but folks should know there are all kinds of sources of depression and anxiety that have nothing to do with monoamine brain receptor expression.
