'Lost to themselves' is how my therapist described it. Not the same as detachment at all. Detachment is an act of grace and an act of will.
Yes Angelica. I would even add that in addition to "Lost to Themselves" is the idea that they are "Lost Within Themselves". So much to the point that they cannot even take a step back and witness the carnage they are creating in their life and in others.
Detaching is a scary process. It is scary because as you detach you wonder if you are letting go too much. It is scary because you may feel like you are allowing your feelings for them to die.
Detaching is really letting go to the extent that what the WAS does to you, says to you, act likes, etc - simply doesn't affect you anymore. Detaching is about being at piece. It is about becoming aware that by interferring and/or pursuing them, you only push them away more. When you finally detach, you focus on you, let them go off and go through whatever is they need to go through. Through this process, the WAS may be able to look (albeit for a very small moment in time) outside themselves and wonder what we are doing. But the choice to come back is up to them and what they do. Once we have detached, we quit interferring with this process and realize that the only thing we can control and fix is our own self.
There are a lot of good resources out there on detaching as have been posted and as someone else has said - you will know when you finally arrive at detachment.