Hmm. Not sure exactly. I have gone from being mellow and having a rather good day to thinking of it.

I think that there are other things that are bothering me still from say early that day, the day before, or even years ago. I have a hard time with things that pop up in my head out of the blue from previous times. (maybe I saw something similar happen, or smelled something that triggered that event). It's weird. I will remember that event and start yelling at myself outloud "Stupid" "Idiot" or start yelling outloud at the other person...not going to write down those words. (Have used them against myself too ) Depending on what it is (or how many times I do this in an hour/day, etc), I can switch to thinking about suicide.
Even sadder, I may still act out when I think of it and actually hit myself over the head, across the face, and even arms or legs.
I just don't know where it comes from exactly. It sort of just 'pops up'. I still need to learn how to stop these thoughts & harms as well.