Nausea is symptom not a disease and many conditions can cause nausea in dogs. Most common symptom of nausea in dogs is drooling or excessive salivation. Some dogs also don't eat due to to nausea. Nausea is usually followed by vomiting. This vomiting can be of digested or undigested food, yellow mucous and sometimes foamy mucous. Persistent nausea and vomiting need vet visit immediately.