That's strange because with many dogs it's the other way around. Where is his crate? Could you possibly put his crate in the bedroom with you so he can see you? What's the quality of his stool during the day? Do you know of anything that does scare your dog? Are there any noises that go on in your home or neighborhood at night that might be scaring him?
This DOES sound stress related but I think if he has diarrhea every night health issues should be explored too. And if he is having diarrhea I would be careful about restricting his water lest he get dehydrated.
This DOES sound stress related but I think if he has diarrhea every night health issues should be explored too. And if he is having diarrhea I would be careful about restricting his water lest he get dehydrated.