Symptoms vary based on illness, but vomiting, diarrhea, lack of appetite, lethargy, increased or infrequent urination, coughing, hair loss, loss of mobility, or any combination thereof can all indicate illness in a dog. Even if a dog does not display any of these symptoms, a sudden change in behavior may be alarming enough to warrant a trip to the vet.

Dogs often vomit for harmless reasons, such as eating too much grass, but if they vomit several times in a day and seem lethargic or behave abnormally, take them to see a veterinarian. Bloody stools are another warning sign that dogs are experiencing severe gastric distress and may have parasites or ulcers.

Dogs can also display symptoms unexpectedly. To prepare for possible emergency situations, consult the veterinarian to find out the clinic's protocol. If the clinic is not open all night, it may be affiliated with an emergency clinic that can be contacted. Pale gums, rapid breathing, change in temperature, seizures and weak pulse are all signs that indicate that emergency care is needed. Some dogs may become aggressive in their distress and need to be approached cautiously.

If symptoms point to poisoning, call the ASPCA Animal Poison Control hotline to consult trained toxicologists for a recommendation on a course of action.