Normally, when you are asleep and dreaming, your body is paralysed. I suppose it’s to stop your muscles working in tune with your dreams and making you sleepwalk (though this does, of course, sometimes happen). And normally, when you wake and your dream vanishes, the paralysis goes and you can move your muscles. But occasionally there is a delay between your mind returning to consciousness and your muscles coming back to life, and that is called sleep paralysis.
