Chills are frequently a symptom of fever, which can be caused by a variety of diseases. Hypothermia and other disorders can also produce chills. Chills are frequently accompanied by additional symptoms that vary depending on the underlying disease, ailment, or condition. For example, people with the flu may have a fever, headache, muscle pain, and cough. Additionally, those who suffer from Lyme disease often experience a rash, joint pain, and mental confusion. If you are having trouble sleeping even though you are tired, have no energy, feel cold all the time, tremble when you walk, and have trouble breathing then you should see your doctor right away because these are all signs of pneumonia. You will need to see your doctor if you have a fever or cough with cold symptoms. These are all warning signs that you may have a serious illness and need medical attention. Severe chills can be a sign of a more serious problem. If you have severe chills and no other symptoms, then this is called "isolated hypothermia." It is not dangerous by itself, but it can be an indicator of another health problem. For example, isolated hypothermia may occur when someone loses their heat quickly by exercising too hard or spending too much time in the cold. If you have chronic fatigue syndrome (CFS) then you may experience chills as one of your symptoms.