That's a really interesting suggestion, MudLily. My symptoms do seem to have a lot in common with the low serotonin symptom lists I can find.
Have you read Paul Jaminet's stuff about the potential dangers of adding in tryptophan or serotonin when you're low? Apparently your body sequesters tryptophan when you have certain kinds of infections and adding more in under those circumstances gives a leg up to the pathogen. I wonder if there's a way to tell whether it's a pathogen or something you did that is causing the low serotonin?
Charlie, that's what I feel like has happened to me! Except it turns on and off really quickly depending on how many carbs I'm eating now, even though it took a month or 6 weeks to show up the first time. Do you happen to know or have any ideas about what the physiological mechanism would be that would cause your stress response to get messed up by low carb?