Different forms of mental illness manifest as a range of different symptoms. Even symptoms of the same or similar disorders can manifest differently from one patient to another. According to Mayo Clinic, mental disorders can affect thoughts, emotions and behaviors.
Mayo Clinic lists a number of symptoms as common signs of the development of mental illness. Among these are depression, confusion, mood swings, unusual or disturbing thoughts, reduced ability to concentrate, withdrawal from activities and social interactions, and excessive fears or worries sometimes with feelings of guilt. Other symptoms, which can be the signal that something serious is wrong, include hallucinations, detachment from reality, trouble relating to other people, difficulty coping with situations and major changes to eating habits, sexual activity or patterns of drug and alcohol consumption. Excessive anger or hostility can also be a sign of a serious mental illness.
Mayo Clinic recommends seeking professional help if any of these symptoms are present, as many mental illnesses persist over time and could get worse without timely treatment. One of the most serious symptoms of mental illness is the development of suicidal thoughts. If this happens, the condition should be treated as a medical emergency demanding immediate medical attention.