I don't know how much I can add to Anna's post, but I will try to explain it from my experience.

I have used dissociation for my than half my life. A lot of times I am the only one who knows I am doing it. I had to really work to finally find a psychologist who could tell when I was dissociating. I can tell the stories of my abuses with no emotion behind them at all. I feel like there is this wall that separates the wife/mom/today me from the abused me. The problem with this is that there are leaks through the wall. I get upset about small trivial things...but don't feel anything about the big things.

When I am talking about abuse, I experience the following:
1) my body feels physically numb
2) I don't feel like I am in my body...but I am not "looking down on the situation"
3) I have a hard time making eye contact
4) My eyes glaze over and I look through people if I am making eye contact

For me, dissociation is a survival mechanism. I am working on learning positive coping skills so I can start to really deal with the abuse that has occured.