In a normal dream situation your brain shuts off the gross motor functions of your limbs, so you don't hurt yourself when you dream. When you're young and the brain isn't fully formed, and at certain developmental stages, like in rapid growth times, that system doesn't work well and your limbs are 'on', hence sleepwalking (and sometimes sleep-making a sandwich). It's known to be hereditary (or at least it runs in families- my brother used to wake up in the bathroom trying to pee against the door- my dad got to handle that. So it's an entirely physical phenomenon. Usually at a certain stage it stops happening, and it could be triggered by nightmares, where the escape impulse is high. So the question is not 'can it be caused by negs', but 'what is causing the nightmares in the first place'?