Some of the signs of more serious conditions in cats and dogs may also be those that present for common conditions, which can make it tough to tell if your pet needs quick treatment or has a more chronic illness. This makes prompt and caring veterinary treatment that much more important. A few of the markers of more serious conditions in pets may include: Vomiting and diarrhea Lack of appetite Lethargy or decreased activity Significant changes in urination habits Coughing Hair loss Trouble moving or getting up