I can only speak to my experience, but I was CONVINCED I had parasites. I thought I had them all throughout my body.
Then I realized I was wrong. How?
Well, at first I was so convinced I told myself, "either I am mentally imagining I have parasites coming out of my body, or I do". I learned how to cut my hair as I was feared they were even coming out of my scalp.
Now ask yourself "were you ever fearful of getting parasites?" It was ALWAYS a fear of mine growing up.
I then got to the point I did not care.
I hit rock bottom and thought that was it. I gave up and thought "well I just have to live with it and see if it kills me". My symptoms then went away.