Thank you very much Ally! It was a little bit of a surprise to me too the first time I had such free movement seconds after being stiff as a board.
I’m not sure I have a short answer for how it’s done, but it seems to be some combination of a few of the following: determination, inspirational place, inspirational cause, inspirational people,  perhaps spontaneously applying movement to a different neural pathway, perhaps internally sparking creation of dopamine, lots of mindful, intense exercise…
I think it could be experimented with by almost anybody though. I’ve since been experimenting with more of this kind of movement with some  modest success. It’s not  ever-reliable. It is, however, really nice to have on occasion. Today on occasion, Eventually the norm?
Our minds and emotions are more powerful than most of us understand.  Don’t let this disease steal your hope.  But do be active, creative, and relentless.