So, your brain is basically shutting down the nervous system of your body’s musculature. This prevents you from moving around in your dreams. Otherwise everybody would be sleepwalking, it doesn’t work right for people that are suffering from that. That’s also where dreams of flying or falling come from as well as sleep paralysis, which is basically your brain shutting down your body while you’re still conscious. Just before your body is shut down, the electric pathways of the nervous system of your musculature are discharged, which can manifest itself as a jolt through your body, ironically waking you up again.