@turkay1-- My sister suffers from sleepwalking. As far as I know, when we sleep, our hindbrain "turns off" our ability for physical movement. In people who sleepwalk, this never gets turned off and they are able to move even though they are asleep. It has to do with the mechanism never fully developing in childhood or not working as well as it used to over time.
However there are some supplements like GABA (a type of amino acid) that help with this mechanism. My sister has been experiencing less instances of sleepwalking since she started taking it.