This symptom in dogs is mostly due to the fact that the dog accumulates a large amount of digestive juice before going to bed, which stimulates the dog's gastrointestinal tract while sleeping, so the dog will vomit immediately after waking up. There are also picky dogs that will produce gastric acid at night because their stomachs are empty, and they will vomit yellow water when they wake up. This situation requires the owner to give the dog some stomach-building and disappearing pills, and it will improve in a few days.