Well, this particular instance is significant because the strangling went on a little too long and when I thought 'all right, maybe I should push her hands off my neck now' I found I had forgotten how to lift my arms or speak, which was a bit alarming. But I can't remember what brought it on.

The pseudo-Freudian part of me is trying to connect this to your Derren Brown fic. The rest of me is trying to give myself a metaphorical whack on the head, and go "This isn't Riona doing asphyxiation fic! This is reality! Be properly alarmed!"

Although I'm guessing you did work out the speaking and arm-lifting thing eventually, or you would have mentioned that by now.