Mental Health and Mental Illness: How to Spot Problems and Get Help Mental health affects nearly everything we do—how we think, feel, make decisions, respond to stress, and connect with other people. It is more than the absence of a psychiatric diagnosis. A person with a diagnosed mental illness may feel stable and well for long periods. Meanwhile, someone without a diagnosis may be struggling with serious emotional distress. Mental health exists on a spectrum, and it can shift throughout a person’s life. Mental illness refers to conditions that cause clinically significant changes in mood, thought, perception, or behavior. These conditions include anxiety disorders, depressive disorders, bipolar disorder, schizophrenia and other psychotic disorders, eating disorders, post-traumatic stress disorder, and substance-use disorders. There is no single way mental illness looks. Symptoms may appear once, return periodically, or continue for years. Two people with the same diagnosis can ...