These words all describe sb who is suffering from a mental illness.以上各词均用以形容患有精神疾病的人。
mentally ill suffering from an illness of the mind, especially in a way that affects the way you think and behave指有精神病
insane[not usually before noun](ratherformal) suffering from a serious mental illness and unable to live in normal society指精神失常、神经错乱：◆The question is, was the man insane when he committed the crime?问题在于这男人犯罪时是否处于精神失常状态？NOTE In informal English insane can describe sb who is not suffering from a mental illness, but whose mind does not work normally, especially because they are under pressure. This meaning is used especially in the phrases go insane and drive sb insane.在非正式英语中，insane 可用于未患精神病但尤因压力导致心智不正常的人。这一含义尤用于 go insane 和 drive sb insane 短语中。
neurotic(medical医学) suffering from or connected with neurosis (= a mental illness in which a person suffers strong feelings of fear and worry)指神经机能病的、神经官能症的：◆the treatment of anxiety in neurotic patients对神经官能症病人焦虑感的治疗NOTEIn informal English neurotic is also used to describe sb who is not suffering from a mental illness, but is not behaving in a calm way because they are worried about sth.在非正式英语中，neurotic 亦用以指未患精神病、但因担忧而变得神经质的人：◆She became neurotic about keeping the house clean.她对保持房子清洁有点神经质。
psychotic(medical医学) suffering from or connected with psychosis (= a serious mental illness in which thought and emotions lose connection with external reality)指精神错乱的、有精神病的NOTE In informal English psychotic is sometimes used to describe anyone suffering from a mental illness, but in correct medical usage it only describes people who have difficulty relating to external reality. It contrasts with neurotic, which describes people who are less seriously mentally ill and are still able to distinguish what is real from what is not.在非正式英语中，psychotic 有时用以泛指患有精神疾病，但在正确的医学用语中，只用以描述难以与客观现实建立联系的人，这与 neurotic 形成对比；neurotic 用以描述患精神错乱程度较轻，仍能区分现实与虚幻的人。
disturbed mentally ill, especially because of very unhappy or shocking experiences指有精神病的、心理不正常的、精神紊乱的，尤因不幸或受刺激所致：◆He works with emotionally disturbed children.他从事跟精神异常儿童有关的工作。
unstable having emotions and behaviour that are likely to change suddenly and unexpectedly指情绪、行为反复无常的、不稳定的