Lethargy is a state of drowsiness, inactivity, or indifference in which there are delayed responses to external stimuli such as auditory (sound), visual (sight), or tactile (touch) stimuli. Lethargy may also refer to the general malaise and decreased activity exhibited by animals that do not feel well.

Lethargy is a nonspecific sign associated with many possible underlying systemic disorders. It may have little to no impact on the affected individual; however its presence may represent severe or life-threatening illness. Lethargy of more than a day's duration should not be ignored, and should be addressed, especially if it persists.

General Causes

Anemia (low red blood cell count)

Other blood disorders

Cardiovascular (heart and vessels) and pulmonary (respiratory) disorders

Chronic inflammation or infection

Drug or medication related

Electrolyte abnormalities
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Endocrine (hormonal) or metabolic disorders

Gastrointestinal diseases

Urinary tract disorders

Cancer

Immune diseases

Certain severe skin diseases

Certain eye diseases, particularly those associated with blindness

Neurologic and neuromuscular disorders

Nutritional disorders

Behavioral disorders

Skeletal diseases

Infectious diseases

Exposure to certain toxins

Physical trauma

What to Watch For

A general change in demeanor

Listlessness

Reluctance to play, exercise or perform normal behaviors

Hiding, avoiding contact with people or other pets

Decrease in appetite or thirst

Gastrointestinal signs (vomiting, diarrhea, weight loss)

Difficulty breathing

Tremors

Weakness

Changes in the level of consciousness

Fever