Across ancient civilizations, dreams carried more than fleeting images; they were interpreted as signals about a person’s health and fate. Early doctors, including the famed Galen, treated dream reports as part of a diagnostic toolkit. In his second-century text On Diagnosis in Dreams, he argues that dream content can reflect underlying bodily states governed by the four humors: blood, phlegm, yellow bile, and black bile.

Galen and his contemporaries believed that balance among these humors determined wellness. They connected dreams with specific ailments: a dream of a blazing fire might point to an excess of yellow bile, whereas smoke or darkness could signify an overabundance of black bile. Likewise, a rainstorm was interpreted as too cold and damp, while snow and ice were seen as manifestations of cold phlegm.

The practice of linking dreams to health was controversial from the start, and Galen defended his approach against critics. Over time, the humoral theory lost ground as medical science shifted toward germ theory and new understandings of disease in the following centuries.

Note: The historical view of dreams as diagnostic tools reveals how medical theories evolve, even when they center on the intimate link between mind, body, and waking life.