My 11month old puppy is fully house trained and has been since a month after we got him. About 2 weeks ago he started dribbling dilute urine in his sleep. He drinks on average 21 cups of water/day. All labs, urinalysis, urine culture, bile acid test have been picture perfect. He doesn't do it when he's awake and we let him out at least every 2 hours. Any ideas why would he be doing this?