The disorder in which patients always think they are sick is known as hypochondria. People with hypochondria experience a persistent belief that they have a serious illness, even if medical evidence of an illness is absent.
MedlinePlus states that hypochondriacs are unable to control the symptoms and worry they experience as a result of this disorder. Many people with hypochondria experienced physical or sexual abuse in their lives. Although people with hypochondria do sometimes feel better and stop worrying, they tend to resume the cycle of symptoms and worrying soon after. Doctors and other health professionals can treat the disorder with cognitive-behavioral therapy or with antidepressants such as selective serotonin reuptake inhibitors.