I have dissociation with my PTSD. It is always a welcome feeling to find other people experience similar things!

One thing I have found is that things that trigger me are not necessarily obvious or directly related to my traumas. For example, feeling cornered or overwhelmed is a major trigger for me, so even things that have nothing to do with my abuse can set me off--like getting extra work or feeling pressured at work. I am also waaaaay more likely to get triggered and end up dissociating if I am tired--it's like it lowers my threshold for coping. It sounds like you had an exhausting day, and something that normally might not push you over the edge into dissociating might have then been able to. Just an idea!