Emotions don't cause parasites, but they can play a role in getting well. Not so much whether you are happy or sad, but when you are stressed and having personal trauma, things happen in your body. Stress releases corisol in the body, and messes with your hormones and in turn, your immune system takes a dive. An immune comprimised, stressed and emotional human is the perfect host for parasites.
In my case, I was exposed to a stomach bacteria. This bacteria is supposed to be found in 80% of humans, and harmless in some (so they say). In my case, I was exposed to it during a very stressful times, which is medically proven to flourish during high stress. This bacteria lowers your stomach acids, which may be the reason that I am still sick, after recovering many times over. The host of this bacteria, is also the stressor. Ain't love grand :)