If your pet turtle is hibernating, it will appear inactive, possibly buried in substrate, and its metabolic rate will slow down. Its heart rate and breathing will decrease significantly to conserve energy. However, if your turtle is sick, you may notice abnormal behaviors such as lack of appetite, lethargy, discolored or swollen eyes, unusual basking patterns, or shell abnormalities. It's important to monitor your pet turtle closely and consult a veterinarian if you suspect it is sick to ensure proper care and treatment.