Hey !

From what I understand, dissociation is a defense mechanism one employs in response to an unpleasant external stimulus which may be perceived as a threat, while derealization is something I wouldn't necessarily associate with unpleasant surroundings ... its cause can be something like epilepsy.

Your experience sounds more like derealization to me than dissociation.

I, personally, can relate more to dissociation, because I experience it (or wish to) almost daily. My dissociation generally kicks in when I see people enjoying each others' company (something I will never get to do). Typically, this is something like couples holding hands or hugging or just going somewhere together in a car. Or a gathering of people just having a good ol' time.

My typical dissociation response is immediate, intense, and consists of one of the following thoughts:
1 - Thinking about my next workout at the gym (my second home, practically) ... which muscles I'm going to exercise, which exercises, to the point where I'm almost lifting weights in my mind.
2 - Thinking about being with God ... not having to drown in the torturous and turbulent pool of jealousy that my stay here is, but being immersed in the ocean of serenity and calm that I know my eternity will be.