I can't say I've ever been familiar with that word.
I think (tho I can't be certain) that I MAY have experienced that state - on a relatively limited time - after certain devastating emotionally traumatic events. Like a true "state of shock", numbness - a postponement of response. The rational cognitive mind keeps working, making decisions, but if you "feel" anything, it is a sense of extremely deep impervious unflappability. It took me some time to "deprocess" once I was away from the scene... but a full emotional response did not develop more at least a week.
Anyway, I have felt that before - very seldom -- but cetainly just 3 weeks ago. But is that what the term means or what it means to you?
What do you think, Tim, has made you (not) feel this way? And has something like this ever happened before?