In my reading, I saw that when someone is recoverying from PTSD, 'sudden startling' (which is a better word for me than twitching) is one of the last symptoms to disappear. It's related to our hypervigilance.

But I find it interesting about so many having facial twitches. When my stress levels go up, I find parts of my face go numb and I get the facial tics as well.

Lisa