Sleeping much more than usual
Loss of interest in playing
Eating less or more than usual
Hiding more often
Reduced grooming or a messy coat
Less social interaction with people or other pets
Changes in vocalizing, such as being unusually quiet
Irritability or unusual aggression
Litter box changes, including accidents outside the box
Restlessness or pacing
Clinginess or seeking constant attention
Weight loss or weight gain
Slow response to favorite toys or treats
Changes after a major household change or loss
Signs lasting more than a few days
Veterinary check needed to rule out illness or pain