Signs of illness are physical or mental indications that something is wrong with a person's health. SYMPTOMS are the most common signs of illness, and can include fever, fatigue, pain, nausea, vomiting, and changes in appetite or behavior. Other signs of illness may include coughing, sneezing, rashes, or difficulty breathing. In some cases, a person may experience a combination of SYMPTOMS, which can be a sign of a more serious underlying condition.