That goes back to my point about the humble electron.

There are a ton of things moving in your body all the time regardless if you are sitting still of not. The only thing that I can think of that would be drastically impacted by instant cancellation of momentum is electrical signals. I admit, that is absolutely pushing the boundaries of what I know about physics at that scale.

Stopping every electrical signal in your body simultaneously and assuming it will just resume spontaneously seems odd to me, is all.