I think anything that causes someone stress can be a trigger for dissociation. Though i am not saying stress alone is the only trigger. I have definently had extreme bouts of depression and anxiety that werent based on any events in particular that i dissociated from (involuntarily) because the feelings were too extreme. I think the main thing that causes dissociation in my personal opinion is a fear of the uncertain or mysterious aspects of life or of a persons experiances.
I definitely agree that fear of uncertaint makes me freak out. If it seems like there isn't a logical explanation for something and that it's magic, I can't deal with it. This is because before all this, I was so certain of my belief that everything had a logical explanation.
For example the problem I've had with this dream premonition thing and all the details surrounding it. I had a dream, something from it then appeared the next day, next night I dream, next morning something from that dream appears. A few weeks later, I started ruminating how that was too weird to be true. Shortly after I have another dream, next morning something from that appears, then I dream the next night, next morning something from that appears.
I just can't get any rest from intricate little seemingly illogical things like this happening. I go round and round thinking how this can happen two nights in a row on two separate occasions, the second being after I've thought about it. It means that despite all the other evidence for this being the real world, I can't believe that because I can't find an answer to this one conundrum which I feel I believe. This is what I mean by saying dissociation from the belief it is mental illness etc: because I don't have a strong feeling towards the evidence being true despite it being there as proof this could be the real world.