I dont know for sure but my dog is the biggest scardey cat ,,,I got him from the pound so im thinking something happened to him and he has ptsd ,, really ,, its sad and im hoping my care of love for him will help him ,,its better than it was but he gets terrified at times when i cant find a reason for him to react this way . when im having a bad day and my bipolar monster is in a rage he is glued to my side ... I love this mutt hes given me a reason to get out of bed daily ,, but he has his own problems ,,poor lil guy