I have DID also, and what you describe is not what I experience either when I switch or when I do the depersonalization/derealization. I do not have the sense of myoclonic jerk as you describe it (good description, by the way). When I switch to another alter, it feels more subtle; I don't have a sense of suddenness.
With depers/dereal I have perhaps the same feel of not being really present. I usually am thinking like crazy though, even if I can't/don't speak. I can also move.

I hope you get some answers.