my boy groodle has peed in his sleep a few times in the last 4 years (his whole life). He is dreaming and then he just does a little pee and doesn't wake up. It has only happened a few times and i think of it like i would if a child wet the bed. It is only once in a while and when he is fast asleep. But if yours has just started doing it, check it out just to put your mind at ease.