Depression is characterized by sadness, loss of interest or pleasure, feelings of guilt or low self-worth, disturbed sleep or appetite, tiredness, and poor concentration. People with depression may also have multiple physical complaints with no apparent physical cause. Depression can be long-lasting or recurrent, substantially impairing people’s ability to function at work or school and to cope with daily life. At its most severe, depression can lead to suicide.
It typically consists of both manic and depressive episodes separated by periods of normal mood. Manic episodes involve elevated or irritable mood, over-activity, rapid speech, inflated self-esteem and a decreased need for sleep. People who have manic attacks but do not experience depressive episodes are also classified as having bipolar disorder.
Psychoses, including schizophrenia, are characterized by distortions in thinking, perception, emotions, language, sense of self and behaviour. Common psychotic experiences include hallucinations (hearing, seeing or feeling things that are not there) and delusions (fixed false beliefs or suspicions that are firmly held even when there is evidence to the contrary). The disorder can make it difficult for people affected to work or study normally
Dementia is usually of a chronic or progressive nature in which there is deterioration in cognitive function (i.e. the ability to process thought) beyond what might be expected from normal ageing. It affects memory, thinking, orientation, comprehension, calculation, learning capacity, language, and judgement. The impairment in cognitive function is commonly accompanied, and occasionally preceded, by deterioration in emotional control, social behaviour, or motivation. Dementia is caused by a variety of diseases and injuries that affect the brain, such as Alzheimer's disease or stroke.
Developmental disorder is an umbrella term covering intellectual disability and pervasive developmental disorders including autism. Developmental disorders usually have a childhood onset but tend to persist into adulthood, causing impairment or delay in functions related to the central nervous system maturation. They generally follow a steady course rather than the periods of remissions and relapses that characterize many mental disorders. Symptoms of pervasive developmental disorders, such as autism, include impaired social behaviour, communication and language, and a narrow range of interests and activities that are both unique to the individual and are carried out repetitively. Developmental disorders often originate in infancy or early childhood. People with these disorders occasionally display some degree of intellectual disability.