I have no idea, but sympathies, that can't be good for sleep.
It isn't like sudden kicks or twitches, just as one is falling asleep? My husband used to do this as part of his sleep apnea, I guess it's the body reacting to the lack of oxygen and kicking to keep him awake? I'm not really sure. Then once a year or so I'll have a week where I do this, I thought I'd learned it from him, but it's part of the MS.
Glad to hear about those improvements.