Mental health problems can present in a wide variety of ways, depending upon the individual and circumstances. It is difficult to define what is 'normal', other than to use an individual's usual behaviour as a point of comparison. Changes in people's mood and personality can provide important indicators as to how they are feeling. Unusual mood swings or social withdrawal might, for example, provide some indication that the person is experiencing some degree of emotional distress. The information below describes the differing types of mental illness and provides links to other sources of information.