Once the chemical-imbalance theory became popular, mental health became synonymous with an absence of symptoms, rather than with a return to a person’s baseline, her mood or personality before and between periods of crisis. Dorian Deshauer, a psychiatrist and historian at the University of Toronto, told me, “Once you abandon the idea of the personal baseline, it becomes possible to think of emotional suffering as relapse—instead of something to be expected from an individual’s way of being in the world.”