Individuals who are perceived to have a mental illness may be forced to accept treatment, such as hospitalization, medication, physical restraints or electroshock. Such coercion is legally permitted if the person is diagnosed as mentally ill and is a danger to self or others. The ability to know whether a person is mentally ill has been shown to be very difficult; nor is there much success in predicting whether someone is a danger. As a practical matter, however, individuals are routinely hospitalized or otherwise treated against their will on the simple say so of the testifying psychiatrist. See Psychiatry: Force of Law by James B. Gottstein, http://psychrights.org/index.htm. Because of the predisposition of many lawyers, judges, testifying psychiatrists and the court system in general to assume that someone contesting treatment is mentally ill and a danger, opposition to forced hospitalization and treatment is difficult. In New York, Mental Hygiene Legal Services, http://www.courts.state.ny.us/courts/ad1/Committees&Programs/MHLS/index.shtml, was set up to represent people who are in a hospital for psychiatric treatment. Each state is different.
Other than forced treatment, individuals who are perceived to have a mental illness face a whole other set of legal issues regarding discrimination and denial of benefits in almost all areas of life, such as employment, SSI and SSD, education, housing. Assistance can be sought at the National Disability Rights Organization (NDRN) - http://www.ndrn.org/index.php and, in each state, a state NDRN agency. [http://www.ndrn.org/en/ndrn-member-agencies.html]