Anxiety is quite often irrational, and therefore you will not be able to predict everything that triggers it.
I've noticed this with my children too - and even had it pointed out by one of my sports-oriented children's coach - who had learned about anxiety in athletes when studying in school.
I will second what everyone else has said - it's not your fault. I also agree with this:
So trying to screen your DS from everything will generally not be useful - unless you know there are things that trigger a reaction. Even for things which are known to trigger anxiety - you will likely want to expose your kids in small doses so that they see they will eventually be OK.
Best wishes,
polarbear