[QUOTE=frost458;1958923So some people can fall asleep while doing those Mantras?[/QUOTE]

If you not too sleepy when going to bed, don't start with mantras, untill you feel like you could fall asleep soon. Otherwise, they will keep you awake. And pick some short and simple mantra, so you don't have to concentrate on it or think about the words. "I'm dreaming" should do.