Loss of interest in play, walks, or favorite activities
Sleeping much more or seeming unusually tired
Eating less or showing changes in appetite
Withdrawing from people or other pets
Lethargy or low energy
Whining, howling, or other unusual vocalizing
Restlessness or pacing
Changes in grooming or self-care
Hiding or seeking isolation
Irritability or unusual aggression
Clinginess or increased neediness
Changes in bathroom habits
Not responding to cues or commands as usual
Signs lasting more than a few days or getting worse
A sudden change after a loss, move, routine change, or absence of a companion
Veterinary checkup if behavior changes are persistent or severe