The dog always shivering slightly when lying down may be caused by feeling cold, catching a cold, timidity, calcium deficiency, high fever, or acute encephalitis. It is best to check the dog's body for other diseases. If If there are no other symptoms, just keep the dog warm; if the dog trembles frequently or has poor energy, loss of appetite, high fever, etc., it is best to send it to a pet hospital for examination and treatment.