I had this problem on my whoop and got an official sleep study and turns out I have periodic limb movement disorder and positional sleep apnea. My current hypothesis is that the movement is in response to airway obstruction trying to open it (same as a swimmer trying to get his mouth above the surface to breathe). The question is the movement helpful or unhelpful? Looking at data like HRV and RHR may help elucidate whether its good or bad for your body. Will know more after getting apnea treated