I'm also convinced of the same thing, I don't know enough about biology, but I have days where I feel like the only thing that could be causing certain emotions is an infection that I don't know about.

For example, I use to feel tired all the time, and I would get sick all the time. I swear I could "feel" that my immune system sucked and I constantly had to fight things off.

Now I feel like my immune system is stronger, and it shows because I get sick so less often. My brain fog is basically gone and my energy levels are a lot higher. Every now and then it comes back, but recently I always wondered:

Is there a set of anti-biotics, anti-parasitical, anti-viral drugs that you could take in a row to try to flush the body of any infections? There's been similar comments about HSV1, that a lot of people have, but there's also Toxoplasmosis. If you look into it, so many people have both of these infections, but what are the side effects on the body?

I think immune system is one part of the picture. I also think your bodies natural response to the environment has something to do with this. I've been way more social and have gotten WAY better social feedback from all angles in my life (positive feedback loop) and that has helped immensely with mood and feeling good all the time.

When you combine a lot of these things, such as: poor immune system, conflicted social life, bad diet, and lack of exercise, I could see how the combination could manifest its self into mental illness.

I'm still convinced pathogens have a high ranking in the cause of brain fog and emotional issues tho, social life being second, diet third and surprisingly exercise being last even though I initially thought it was number 1. It just made me feel good, but it didn't really get to the root of any issue for some reason.